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THE DIFFERENT FORMS OF FLOWERS ON PLANTS 


MON 


THE 


DIFFERENT FORMS OF FLOWERS 


ON 


PLANTS OF THE SAME SPECIES. 


By CHARLES DARWIN, M.A., F.RB.S. 


WITH ILLUSTRATIONS. 


NEW YORK: 
‘D. APPLETON AND COMPANY, 
549 AND 551 BROADWAY. 
oT % 


 5YL.I5 
gi yee Bisley 
re 


To 
PROFESSOR ASA GRAY 
Chis Volume is Dedicated 


BY THE AUTHOR 


AS A SMALL TRIBUTE OF RESPECT AND 
AFFECTION. 


438692 


¢ 


Digitized by the Internet Archive 
in 2010 with funding from 
University of Illinois Urbana-Champaign 


http://www.archive.org/details/differentformsof01darw 


CONTENTS. 


INTRODUCTION eS esi set teoylste Duet . oa baged=13 


CHAPTER L 
HETEROSTYLED DimorpHic PLANTS: PRIMULACER. 


Primula veris or the Cowslip—Differences iu structure between the 
two forms—Their degrees of fertility when legitimately and ille- 
gitimately united—P. elatior, vulgaris, Sinensis, auricula, &c.— 
Summary on the fertility of the heterostyled species of Primula— 
Homostyled species of Primula—Hottonia palustris—A ndrosace 
Vitalliana BE Seca aah ie heed aol dat) pete won PL oee 


CHAPTER II. 
Hysrip PrRIMULAS. 


The Oxlip a hybrid naturally produced between Primula veris and 
vulgaris—The differences in structure and function between the 
two parent-species—Effects of crossing long-styled and short- 
styled Oxlips with one another and with the two forms of both 
parent-species—Character of the offspring from Oxlips artificially 
self-fertilised and cross-fertilised in a state of nature—Primula 
elatior shown to be a distinct species—Hybrids between other 
heterostyled species of Primula—Supplementary note on spon- 
taneously produced hybrids in the genus Verbascum .. 55-80 


vi CONTENTS. 


CHAPTER 122 
HetTeRostyLeD DimorpHic PLANTS—continued. 


Linum grandiflorum, long-styled form utterly sterile with own-form 
pollen—Linum perenne, torsion of the pistils in the long-styled 
form alone—Homostyled species of Linum—Pulmonaria oflici- 
nalis, singular difference in self-fertility between the English 
and German long-styled plants—Pulmonaria angustifolia shown 
to be a distinct species, long-styled form completely self-sterile— 
Polygonum fagopyrum—Various other heterostyled genera— 
Rubiacex—Mitchella repens, fertility of the flowers in pairs— 
Houstonia—Faramea, remarkable difference in the pollen-grains 
of the two forms; torsion of the stamens in the short-styled 
form alone; development not as yet perfect—The heterostyled 
structure in the several Rubiaceous genera not due to descent in 
COMMION 65 uy de es, de: ces _ ce, ae 


CHAPTER LY. 
HETEROSTYLED TRIMORPHIC PLANTS. 


Lythrum salicaria—Description of the three forms—Their power and 
complex manner of fertilising one another—Highteen different 
unions possible—Mid-styled form eminently feminine in nature 
—Lythrum Grefferi likewise trimorphic—L. thymifolia dimor- 
phic—L. hyssopifolia homostyled—Nesaa verticillata trimorphic 
—Lagerstremia, nature doubtful—Oxalis, trimorphic species of 
—O. Valdiviana—O. Regnelli, the illegitimate unions quite 
barren—O, speciosa—O, sensitiva—Homostyled species of Oxalis 
—Pontederia, the one monocotyledonous genus known to include 
heterostyled species” .. .. o» -. o- ss om) hau cue 


OW AP TER NV; 
ILLEGITIMATE OFFSPRING OF HeTEerosTyLeD PLANTS. 


Illegitimate offspring from all three forms of Lythrum salicaria— 
Their dwarfed stature and sterility, some utterly barren, some 


CONTENTS. vii 


fertile—Oxalis, transmission of form to the legitimate and il- 
legitimate seedlings— Primula Sinensis, illegitimate offspring in 
some degree dwarfed and mfertile—Equal-styled varieties of P. 
Sinensis, auricula, farinosa, and elatior—P. vulgaris, red-flowered 
variety, illegitimate seedlings sterile—P. veris, illegitimate 
plants raised during several successive generations, their dwarfed 
stature and sterility—Equal-styled varieties of P. veris—Trans- 
mission of form by Pulmonaria and Polygonum—Concluding 
remarks—Close parallelism between illegitimate fertilisation and 
PUM tk Kak ee as vs ve we | ea 189-243 


OR APP EHR: VE: 
ConcLupiInG REMARKS ON HETEROSTYLED PLANTS. 


The essential character of heterostyled plants—Summary of the 
differences in fertility between legitimately and illegitimately 
fertilised plants—Diameter of the pollen-grains, size of anthers 
and structure of stigma in the different forms—Affinities of the 
genera which include heterostyled species—Nature of the 
advantages derived from heterostylism—The means by which 
plants became heterostyled—Transmission of form—Equal- 
styled varieties of heterostyled plants—Final remarks 244-277 


CHAPTER VII. 


PotyGamous, Diacious, AND GyNo-piccrous PLANTs, 


The conversion in various ways of hermaphrodite into dicecious 
plants—Heterostyled plants rendered dicecious—Rubiacew— 
Verbenaceex—Polygamous and sub-dicecious plants—Euonymus 
—Fragaria—The two sub-forms of both sexes of Rhamnus and 
Epigea—Ilex—Gyno-dicecious plants—Thymus, difference in 
fertility of the hermaphrodite and female individuals—Satureia 
—Manner in which the two forms probably originated—Scabiosa 
and other gyno-dicecious plants—Difference in the size of the 
corolla in the forms of polygamous, dicecious, and gyno-dicecious 
UP RNs es Saal ek on.) os - ss) at ae LOCUS 


vill CONTENTS 


CHAPTER OVELL 
CLEISTOGAMIC FLOWERS. 


General character of cleistogamic flowers— List of the genera pro- 
ducing such flowers, and their distribution in the vegetable 
series—Viola, description of the cleistogamic flowers in the 
several species; their fertility compared with that of the perfect 
flowers—Oxalis acetosella—O. sensitiva, three forms of cleisto- 
gamic flowers—Vandellia—Ononis—Im patiens—Drosera— Mis- 
cellaneous observations on various other cleistogamic plants— 
Anemophilous species producing cleistogamic flowers—Leersia, 
perfect flowers rarely developed—Summary and concluding 
remarks on the origin of cleistozamic flowers—The cnief con- 
clusions which may be drawn from the observations in this 
volume ca be ae Te Se es, ees ashy Ue 


INDEX oe oe ee oe es ee oe ee oe ee oe 346-352 


THE 


DIFFERENT FORMS OF FLOWERS 


ON 


PLANTS OF THE SAME SPECIES. 


INTRODUCTION. 


THE subject of the present volume, namely the dif- 
ferently formed flowers normally produced by certain 
kinds of plants, either on the same stock or on distinct 
stocks, ought to have been treated by a professed bota- 
nist, to which distinction can lay no claim. As far as 
the sexual relations of flowers are concerned, Linnzeus 
long ago divided them into hermaphrodite, moncecious, 
dicecious, and polygamous species. This fundamental 
distinction, with the aid of several subdivisions in each 
of the four classes, will serve my purpose; but the 
classification is artificial, and the groups often pass 
into one another. 

The hermaphrodite class contains two interesting 
sub-groups, namely, heterostyled and cleistogamic 
plants; but there are several other less important 
subdivisions, presently to be given, in which flowers 
differing in various ways from one another are pro- 
duced by the same species. 

Some plants were described by me several years ago, 
ina series of papers read before the Linnean Society,* 


* “On the Two Forms or Di- of Primula, and on their remark- 
morphic Condition in the Species able Sexual Relations.” ‘Journal 


2 INTRODUCTION. 


of which exist under two or three 
forms, differing in the length of their pistils and 
stamens and in other respects. They were called by 
me dimorphic and trimorphic, but have since been 
better named by Hildebrand, heterostyled.* As I 
have many still unpublished observations with respect 
to these plants, it has seemed to me advisable to re- 
publish my former papers in a connected and cor- 
rected form, together with the new matter. It will be 
shown that these heterostyled plants are adapted for 
reciprocal fertilisation ; so that the two or three forms, 
though all are hermaphrodites, are related to one 
another almost like the males and:females of ordinary 
unisexual animals. I will also give a full abstract of 
such observations as have been published since the 
appearance of my papers; but only those cases will be 
noticed, with respect to which the evidence seems fairly 
satisfactory. Some plants: haye been supposed to be 
heterostyled merely from their pistils and stamens 
varying greatly in length, and I have been myself 
more than once thus deceived. With some species the 


the individuals 


of the Proceedings of the Linnean 
Society,’ vol. vi. 1862, p. 77. 

“On the Existence of Two 
Forms, and on their Reciprocal 
Sexual Relation, in several Species 
of the Genus Linum.” Ibid. vol. 
vii. 1863, p. 69. 

“ On the Sexual Relations of the 
Three Forms of Lythrum salicaria,’ 
Ibid. vol. viii. 1864, p. 169. 

“ On the Character and Hybrid- 
like Nature of the Offspring from 
the Illegitimate Unions of Dimor- 
phic and Trimorphie Plants.” 
Ibid. vol. x. 1868, p. 393. 

“On the Specific Differences 
between Primula veris, Brit. Fl. 
(var. officinalis, Linn.), P. vulgaris, 
Brit. Fl. (var. acaulis, Linn.), and 


P. elatior, Jacq.; and on tho 
Hybrid Nature of the Common 
Oxlip. With Supplementary Re- 
marks on Naturally Produced Hy- 
brids in the Genus Verbascum.” 
Ibid. vol. x. 1868, p. 437. 

* The term “ heterostyled ” does 
not express all the differences be- 
tween the forms; but this is a 
failure common in raany cases. 
As the term has been adopted by 
writers in various countries, I am 
unwilling to change it for that of 
heterogone or heterogonous, though 
this has been proposed by so high 
an authority as Prof. Asa Gray: 
see the ‘American Naturalist,’ 
Jan. 1877, p. 42. 


INTRODUCTION. 5 


pistil continues growing for a long time, so that if old 
and young flowers are compared they might be thought 
to be heterostyled. Again, a species tending to become 
dicecious, with the stamens reduced in some individuals 
and with the pistils in others, often presents a decep- 
tive appearance. Unless it be proved that one form 
is fully fertile only when it igs fertilised with pollen 
from another form, we have not complete evidence 
that the species is heterostyled. But when the pistils 
and stamens differ in length in two or three sets of - 
individuals, and this is accompanied by a difference in 
the size of the pollen-grains or in the state of the 
stigma, we may infer with much safety that the species 
is heterostyled. I have, however, occasionally trusted 
to a difference between the two forms in the length 
of the pistil alone, or in the length of the stigma 
together with its more or less papillose condition ; and 
in one instance differences of this kind have been 
proved by trials made on the fertility of the two forms, 
to be sufficient evidence. 

The second sub-group above referred to consists of 
hermaphrodite plants, which bear two kinds of flowers 
—the one perfect and fully expanded—the other mi- 
nute, completely closed, with the petals rudimentary, 
ofteh with some of the anthers aborted, and the re- 
maining ones together with the stigmas much reduced 
in size; yet these flowers are perfectly fertile. They 
have been called by Dr. Kuhn* cleistogamic, and they 


* «Botanische Zeitung,’ 1867, 
p. 65. Several plants are known 
occasionally to produce flowers 
destitute of a corolla; but they 
belong to a different class of 
eases from cleistogamic flowers. 
This deficiency seems to result 
from the conditions to which the 
plants have heen subjected, and 


partakes of the nature of a mon- 
strosity. All the flowers on the 
same plant are commonly affected 
in the same manner. Such cases, 
though they have sometimes been 
ranked as cleistogamic, do not 
come within our present scope : 
sce Dr. Maxwell Masters, ‘ Vege- 
table Teratology,’ 1869, p. 403. 


4 INTRODUCTION. 


will be described in the last chapter of this volume. 
They are manifestly adapted for self-fertilisation, which 
is effected at the cost of a wonderfully small expendi- 
ture of pollen; whilst the perfect flowers produced by 
the same plant are capable of cross-fertilisation. Cer- 
tain aquatic species, when they flower beneath the 
water, keep their corollas closed, apparently to protect 
their pollen; they might therefore be called cleisto- 
gamic, but for reasons assigned in the proper place are 
not included in the present sub-group. Several cleis- 
togamic species, as we shall hereafter see, bury their 
ovaries or young capsules in the ground; but some few 
other plants behave in the same manner; and, as they 
do not bury all their flowers, they might have formed 
a small separate subdivision. 

Another interesting subdivision consists of certain 
plants, discovered by H. Miiller, some individuals 
of which bear conspicuous flowers adapted for cross- 
fertilisation by the aid of insects, and others much 
smaller and less conspicuous flowers, which have often 
been slightly modified so as to ensure self-fertilisation. 
Lysimachia vulgaris, Euphrasia officinalis, Rhinanthus 
erista-galli, and Viola tricolor come under this head.* 
The smaller and less conspicuous flowers are not closed, 
but as far as the purpose which they serve is *con- 
cerned, namely, the assured propagation of the species, 
they approach in nature cleistogamic flowers ; but they 
differ from them by the two kinds being produced on 
distinct plants. 

With many plants, the flowers towards the outside of 
the inflorescence are much larger and more conspicu- 
ous than the central ones. As I shall not have occa- 


* H. Miiller, ‘ Nature,’ Sept. 25,  * Die Befruchtung der Blumen, 
1873 (vol. viii.), p. 483, and Nov. &c., 1873, p. 294. 
20, 1873 (vol. ix.), p. 44. Also 


- 
a eee eee 


— 


INTRODUCTION. 5 


sion to refer to plants of this kind in the following 
| chapters, I will here give a few details respecting them. 
_ It is familiar to every one that the ray-florets of the 
Composite often differ remarkably from the others ; and 
so it is with the outer flowers of many Umbellifere, 
some Crucifere and a few other families. Several 
species of Hydrangea and Viburnum offer striking 
instances of the same fact. The Rubiaceous genus 
Musszenda presents a very curious appearance from 
some of the flowers having the tip of one of the sepals 
developed into a large petal-like expansion, coloured 
either white or purple. The outer flowers in several 
Acanthaceous genera are large and conspicuous but 
sterile ; the next in order are smaller, open, moderately 
fertile and capable of cross-fertilisation; whilst the 
central ones are cleistogamic, being still smaller, closed 
and highly fertile; so that here the inflorescence con- 
sists of three kinds of flowers.* From what we know 
in other cases of the use of the corolla, coloured bractex, 
&c., and from what H. Miller has observedt on the 
frequency of the visits of insects to the flower-heads of 
the Umbelliferee and Composits being largely deter- 
mined by their conspicuousness, there can be no doubt 
that the increased size of the corolla of the outer 
flowers, the inner ones being in all the above cases 
small, serves to attract insects. The result is that 
cross-fertilisation is thus favoured. Most flowers wither 
soon after being fertilised, but Hildebrand statest that 
the ray-florets of the Composite last for a long time, 
until all those on the disc are impregnated; and this 
clearly shows the use of the former. The ray-florets, 


* J. Scott,‘ Journal of Botany,’ men,’ pp. 108, 412. 
London, new series, vol, i. 1872, t See his interesting memoir, 
pp. 161-164. ‘Ueber die Geschlechtsverhiiltnisse 
¢ ‘Die Befruchtung der Blu- bei den Compositen,’ 1869, p. 92. 


6 INTRODUCTION. 


however, are of service in another and very different 
manner, namely, by folding inwards at night and 
during cold rainy weather, so as to protect the florets 
of the disc.* Moreover they often contain matter 
which is excessively poisonous to insects, as may be 
seen in the use of flea-powder, and in the case of 
Pyrethrum, M. Belhomme has shown that the ray- 
florets are more poisonous than-the disc-florets in the 
ratio of about three to two. We may therefore believe 
that the ray-florets are useful in protecting the flowers 
from being gnawed by insects. 

It is a well-known yet remarkable fact that the cir- 
cumferential flowers of many of the foregoing plants 
have both their male and female reproductive organs 
aborted, as with the Hydrangea, Viburnum and certain 
Compositze; or the male organs alone are aborted, as 
in many Composite. Between the sexless, female and 
hermaphrodite states of these latter flowers, the finest 
gradations may be traced, as Hildebrand has shown. tf 
He also shows that there is a close relation between 
the size of the corolla in the ray-florets and the degree 
of abortion in their reproductive organs. As we have 
good reason to believe that these florets are highly 
serviceable to the plants which possess them, more 
especially by rendering the flower-heads conspicuous 


* Kerner clearly shows that 
this is the case : ‘ Die Schatzmittel 
des Pollens,’ 1873, p. 28. 

‘+ ‘Gardener’s Chronicle, 1861, 
p. 1067. Lindley, ‘ Vegetable 
Kingdom, on Chrysanthemum, 
1853, p. 706. Kerner in his in- 
teresting essay (‘ Die Schutzmittel 
der Bliithen gegen unberufene 
Giste,’ 1875, p. 19) insists that 
the petals of most plants contain 
matter which is offensive to in- 
sects, so that they are seldom 


gnawed, and thus the organs of 
fructification are protected. My 
grandfather in 1790 (‘Loves of 
the Plants,’ canto iii. note to lines 
184, 188) remarks that “The 
flowers or petals of plants are 
perhaps in general more acrid 
than their leaves; hence they are 
much seldomer eaten by insects.” 

t¢ ‘Ueber die Geschlechtsver- 
haltnisse bei den Compositen,’ 
1869, pp. 78-91. 


INTRODUCTION. 7 


to insects, it is a natural inference that their corollas 
haye been increased in size for this special purpose ; 
and that their development has subsequently led, 
through the principle of compensation or balance- 
ment, to the more or less complete reduction of the 
reproductive organs. But an opposite view may be 
maintained,* namely, that the reproductive organs 
first began to fail, as often happens under cultiva- 
tion,* and, as a consequence, the corolla became, 
through compensation, more highly developed. This 
view, however, is not probable, for when hermaphrodite 
plants become dicecious or gyno-dicecious—that is, 
are converted into hermaphrodites and females—the 
corolla of the female seems to be almost invariably 
reduced in size in consequence of the abortion of the 
male organs. The difference in the result in these two 
classes of cases, may perhaps be accounted for by the 
matter saved through the abortion of the male organs in 
the females of gyno-dicecious and dicecious plants being 
directed (as we shall see in a future chapter) to the for- 
mation of an increased supply of seeds; whilst in the 
ease of the exterior florets and flowers of the plants 
which we are here considering, such matter is expended 
in the development of a conspicuous corolla. Whether 
in the present class of cases the corolla was first af- 
fected, as seems to me the more probable view, or the 
reproductive organs first failed, their states of develop- 
ment are now firmly correlated. We see this well illus- 
trated in Hydrangea and Viburnum; for when these 
plants are cultivated, the corollas of both the interior 
and exterior flowers become largely developed, and 
their reproductive organs are aborted. 


* I have discussed this subject xviii. 2nd edit. vol. ii. pp. 152, 
in my ‘ Variation of Animals and 156. 
Plants under Domestication,’ chap. 


8 INTRODUCTION. 


There is a closely analogous subdivision of plants, 
including the genus Muscari (or Feather Hyacinth) 
and the allied Bellevalia, which bear* both perfect 
flowers and closed bud-like bodies that never expand. 
The latter resemble in this respect cleistogamic 
flowers, but differ widely from them in being sterile 
and conspicuous. Not only the aborted flower-buds 
and their peduncles (which are elongated apparently 
through the principle of compensation) are brightly 
coloured, but so is the upper part of the spike— 
all, no doubt, for the sake of guiding insects to the 
inconspicuous perfect flowers. From such cases as 
these we may pass on to certain Labiatz, for instance, 
Salvia Horminum, in which (as I hear from Mr. Thisel- 
ton Dyer) the upper bracts are enlarged and brightly 
coloured, no doubt for the same purpose as before, with 
the flowers suppressed. 

In the Carrot and some allied Umbelliferee, the cen- 
tral flower has its petals somewhat enlarged, and these 
are of a dark purplish-red tint; but it cannot be sup- 
posed that this one small flower makes the large white 
umbel at all more conspicuous to insects. The cen- 
tral flowers are said* to be neuter or sterile, but I 
obtained by artificial fertilisation a seed (fruit) appa- 
rently perfect from one such flower. Occasionally two 
or three of the flowers next to the central one are simi- 
larly characterised ; and according to Vaucherf “ cette 
singuliére dégénération s’étend quelquefois 4 ’ombelle 
entiére.” That the modified central flower is of no 
functional importance to the*plant is almost certain. 
It may perhaps be a remnant of a former and ancient 
condition of the species, when one flower alone, the 


* ‘The English Flora, by Sir d’Europe,’ 1841, tom. ii. p. 614. 
J. i. Smith, 182+, vol. ii. p. 39. On the Echinophora, p. 627. 
+ ‘Hist. Phys. des Plantes 


INTRODUCTION. 9 


central one, was female and yielded seeds, as in the 
umbelliferous genus Echinophora. There is nothing 
surprising in the central flower tending to retain its 
former condition longer than the others; for when ir- 
regular flowers become regular or peloric, they are apt 
to be central ; and such peloric flowers apparently owe 
their origin either to arrested development—that is, to 
the preservation of an early stage of development—or 
to reversion. Central and perfectly developed flowers 
in not a few plants in their normal condition (for in- 
stance, the common Rue and Adoxa) differ slightly in 
structure, as in the number of the parts, from the other 
flowers on the same plant. All such cases seem con- 
nected with the fact of the bud which stands at the 
end of the shoot being better nourished than the 
others, as it receives the most sap.* 

The cases hitherto mentioned relate to hermaphro- 
dite species which bear differently constructed flowers ; 
but there are some plants that produce differently 
formed seeds, of which Dr. Kuhn has given a list.f 
With the Umbelliferee and Composite, the flowers that 
produce these seeds likewise differ, and the differences 
in the structure of the seeds are of a very important 
nature. The causes which have led to differences in 
the seeds on the same plant are not known; and it is 
very doubtful whether they subserve any special end. 


We now come to our second Class, that of moncecious 
species, or those which have their sexes separated but 
borne on the same plant. The flawers necessarily 
differ, but when those of one sex include rudiments 


* This whole subject, including Domestication, chap. xxvi. 2nd 
pelorism, has been discussed, and edit. vol. ii. p. 338. 
references given, in my * Variation + ‘Bot. Zeitung,’ 1867, p. 67. 
of Animals and Plants under 


10 INTRODUCTION. 


of the other sex, the difference between the two kinds 
is usually not great. When the difference is great, 
as we see in catkin-bearing plants, this depends 
largely on many of the species in this, as well as in 
the next or dicecious class, being fertilised by the 
aid of the wind;* for the male flowers have in this 
case to produce a surprising amount of incoherent 
pollen. Some few moncecious plants consist of two 
bodies of individuals, with their flowers differing in 
function, though not in structure; for certain indivi- 
duals mature their pollen before the female flowers on 
the same plant are ready for fertilisation, and are called 
proterandrous ; whilst conversely other individuals, 
called proterogynous, have their stigmas mature before 
their pollen is ready. The purpose of this curious func- 
tional difference obviously is to favour the cross-fertili- 
sation of distinct plants. A case of this kind was first 
observed by Delpino in the Walnut (Juglans regia), and 
has since been observed with the common Nut (Corylus 
avellana). I may add that according to H. Miller the 
individuals of some few hermaphrodite plants differ in 
a like manner; some being proterandrous and others 
proterogynous.t On cultivated trees of the Walnut and 
Mulberry, the male flowers have been observed to abort 
on certain individualst, which have thus been converted 
into females; but whether there are any species in a 
state of nature which co-exist as moncecious and female 
individuals, I do not know. 


The third Class consists of dicecious species, and the 


* Delpino, ‘Studi sopra uno 


xi. p. 507, and 1875, p. 26. On 
Lignaggio Anemofilo.’ Firenze, 


proterandrous and proterogynous 


1871. 

¢ Delpino, ‘Ult. Osservazioni 
sulla Dicogamia,’ part ii. fase. ii. 
p. 337. Mr. Wetterhan and H. 
Miiller on Corylus, ‘ Nature,’ vol. 


hermaphrodite individuals of the 
same species, see H. Miiller, ‘ Die 
Befruchtung,’ &e., pp. 285, 339. 

t ‘Gardener’s Chron.’ 1847, pp. 
541, 558. 


INTRODUCTION. 1} 


remarks made under the last class with respect to the 
amount of difference between the male and female 
flowers are here applicable. It is at present an in- 
explicable fact that with some dicecious plants, of 
which the Restiaceze* of Australia and the Cape of 
Good Hope offer the most striking instance, the dif- 
ferentiation of the sexes has affected the whole plant 
to such an extent (as I hear from Mr. Thiselton Dyer) 
that Mr. Bentham and Professor Oliver have often 
found it impossible to match the male and female spe- 
cimens of the same species. In my seventh chapter 
some observations will be given on the gradual con- 
version of heterostyled and of ordinary hermaphrodite 
plants into dicecious or sub-dicecious species. 


The fourth and last Class consists of the plants which 
were called polygamous by Linnzeus; but it appears to 
me that it would be convenient to confine this term to 
the species which co-exist as hermaphrodites, males and 
females; and to give new names to several other com- 
binations of the sexes—a plan which I shall here 
follow. Polygamous plants, in this confined sense of 
the term, may be divided into two sub-groups, accord- 
ing as the three sexual forms are found on the same 
individual or on distinct individuals. Of this latter or 
trioicous sub-group, the common Ash (Frawinus ex- 
célsior) offers a good instance: thus, I examined during 
the spring and autumn fifteen trees growing in the 
same field; and of these, eight produced male flowers 
alone, and in the autumn not a single seed ; four pro- 
duced only female flowers, which set an abundance of 
seeds; three were hermaphrodites, which had a dif- 
ferent aspect from the other trees whilst in flower, and 
two of them produced nearly as many seeds as the 
female trees, whilst the third produced none, so that it 


12 INTRODUCTION. 


was in function a male. The separation of the sexes, 
however; is not complete in the Ash; for the female 
flowers include stamens, which drop off at an early 
period, and their anthers, which never open or dehisce, 
generally contain pulpy matter instead of pollen. On 
some female trees, however, I found a few anthers con- 
taining pollen-grains apparently sound. On the male 
trees most of the flowers include pistils, but these like- 
wise drop off at an early period; and the ovules, which 
ultimately abort, are very small compared with those 
in female flowers of the same age. 

Of the other or monoicous sub-group of polygamous 
_ plants, or those which bear hermaphrodite, male and 
female flowers on the same individual, the common 
Maple (Acer campestre) offers a good instance; but 
Lecoq states * that some trees are truly dicecious, and 
this shows how easily one state passes into another. 

A considerable number of plants generally ranked 
as polygamous exist under only two forms, namely, as 
hermaphrodites and females; and these may be called 
gyno-dicecious,-of which the common Thyme offers a 
good example. In my seventh chapter I shall give 
some observations on plants of this nature. Other 
species, for instance several kinds of Atriplex, bear on 
the same plant hermaphrodite and female flowers; and 
these might be called gyno-monececious, if a name were 
dasieable, for them. 

Again there are plants which produce hee 
and male flowers on the same individual, for in- 
stance, some species of Galium, Veratrum, &c.; and 
these might be called andro-moneecious. If there 
exist plants, the individuals of which consist of her- 
maphrodites and males, these might be distinguished 


* ‘ Géographie Botanique,’ tom. v. p. 367. 


INTRODUCTION. 13 


es andro-dicecious. But, after making inquiries from 
several botanists, I can hear of no such cases. Lecoq, 
however, states,* but without entering into full details, 
that some plants of Caltha palustris produce only male 
flowers, and that these live mingled with the her- 
maphrodites. The rarity of such cases as this last one 
is remarkable, as the presence of hermaphrodite and 
male flowers on the same individual is not an un- 
usual occurrence; it would appear as if nature did 
not think it worth while to devote a distinct indi- 
vidual to the production of pollen, excepting when 
this was indispensably necessary, as in the case of 
dicecious species. 

I have now finished my brief sketch of the several 
cases, as far as known to me, in which flowers differing 
in structure or in function are produced by the same 
species of plant. Full details will be given in the fol- 
lowing chapters with respect to many of these plants. 
I will begin with the heterostyled, then pass on to 
certain dicecious, sub-dicecious, and polygamous species, 
and end with the cleistogamic. For the convenience of - 
the reader, and to save space, the less important cases 
and details have been printed in smaller type. 

I cannot close this Introduction without expressing 
my warm thanks to Dr. Hooker for supplying me with 
specimens and for other aid; and to Mr. Thiselton 
Dyer and Professor Oliver for giving me much in- 
formation and other assistance. Professor Asa Gray, 
also, has uniformly aided me in many ways. To Fritz 
Miller of St. Catharina, in Brazil, I am indebted for 
many dried flowers of heterostyled plants, often accom- 
panied with valuable notes. 


* *Géographie Botanique,’ tom. iv. p. 488. 


14 HETEROSTYLED DIMORPHIC PLANTS. Cuap. L. 


CHAPTER I. 
HETEROSTYLED DiworpHICc PLANTS; PRIMULACEZ. 


Primula veris or the Cowslip—Differences in structure between the 
two forms—Their degrees of fertility when legitimately and ille- 
gitimately united—P. elatior, vulgaris, Sinensis, auricula, &e.— 
Summary on the fertility of the heterostyled species of Primula— 
Homostyled species of Primula—Hottonia palustris—Androsace 
Vitalliana. 


lr has long been known to botanists that the common 
Cowslip (Primula veris, Brit. Flora, var. officinalis, 
Lin.) exists under two forms, about equally numerous, 
which obviously differ from each other in the length 
of their pistils and stamens.* This difference has 
hitherto been looked at as a case of mere varia- 
bility, but this view, as we shall presently see, is far 
from the true one. Florists who cultivate the Polyan- 
thus and Auricula have long been aware of the two 
kinds of flowers, and they call the plants which dis- 
play the globular stigma at the mouth of the corolla, 
“pin-headed” or “ pin-eyed,” and those which display 
the anthers, “thrum-eyed.”t I will designate the two 
forms as the long-styled and short-styled. 

The pistil in the long-styled form is almost exactly 
twice as long as that of the short-styled. The stigma 


* This fact, according to von 
Mob! (‘Bot. Zeitung,’ 1863, p. 326) 
was first observed by Persoon in 
the year 1794. 

+ In Johnson’s Dictionary, 
thrum is said to be the ends of 
weavers’ threads; and I suppose 


that some weaver who cultivated 
the polyanthus invented this name, 
from being struck with some degree 
of resemblance between the cluster 
of anthers in the mouth of the 
corolla and the ends of his 
threads, 


Cuap. I PRIMULA VERIS. 13 


stands in the mouth of the corolla or projects just 
above it, and is thus externally visible. It stands 
high above the anthers, which are situated halfway 
down the tube and cannot be easily seen. In the 
short-styled form the anthers are attached near the 
mouth of the tube, and therefore stand above the 
stigma, which is seated in about the middle of the 
tubular corolla. The corolla itself is of a different 


Long-styled form. Short-styled form, 


PRIMULA VERIS. 


shape in the two forms; the throat or expanded 
portion above the attachment of the anthers being 
much longer in the long-styled than in the short- 
styled form. Village children notice this difference, 
as they can best make necklaces by threading and 
slipping the corollas of the long-styled flowers into 
one another. But there are much more important 
differences. The stigma in the long-styled form 
2 


16 HETEROSTYLED DIMORPHIC PLANTS. OCuaapr. L 


is globular; in the short-styled it is depressed on 
the summit, so that the longitudinal axis of the 
former is sometimes nearly double that of the latter. 
Although somewhat variable in shape, one difference 
is persistent, namely, in roughness: in some speci- 
mens carefully compared, the papilla which render 
the stigma rough were in the long-styled form from 
twice to thrice as long as in the short-styled. The 
anthers do not differ in size in the two forms, which 
I mention because this is the case with some hetero- 
styled plants. The most remarkable difference is in 
the pollen-grains. I measured with the micrometer 
many specimens, both dry and wet, taken from plants 
growing in different situations, and always found a 
palpable difference. The grains distended with water 
from the short-styled flowers were about :038 mm. 
(49-11 of an inch) in diameter, whilst those from the 


7000 
long-styled were about *0254 mm. (~7— of an inch), 


which is in the ratio of 100 to 67. The pollen-grains 
therefore from the longer stamens of the short-styled 
form are plainly larger than those from the shorter 
stamens of the long-styled. When examined dry, 
the smaller grains are seen under a low power to 
be more transparent than the larger grains, and 
apparently in a greater degree than can be ac- 
counted for by their less diameter. There is also a 
difference in shape, the grains from the short-styled 
plants being nearly spherical, those from the long- 
styled being cblong with the angles rounded; this 
difference disappears when the grains are distended 
with water. The long-styled plants generally tend 
to flower a little before the short-styled: for instance, 
I had twelve plants of each form growing in separate 
pots and treated in every respect alike; and at the 
time when only a single short-styled plant was in 


Cuar. I. PRIMULA VERIS. 17 


flower, seven of the long-styled had expanded their 
flowers. 

We shall, also, presently see that the short-styled 
plants produce more seed than the long-styled. It is 
remarkable, according to Prof. Oliver,* that the ovules 
in the unexpanded and unimpregnated flowers of the 
latter are considerably larger than those of the short- 
styled flowers; and this I suppose is connected with the 
long-styled flowers producing fewer seeds, so that the 
ovules have more space and nourishment for rapid 
development. 

To sum up the differences :— The long-styled plants 
have a much longer pistil, with a globular and much 
rougher stigma, standing high above the anthers. The 
stamens are short; the grains of pollen smaller and 
oblong in shape. The upper half of the tube of the 
corolla is more expanded. The number of seeds pro- 
duced is smaller and the ovules larger. The plants 
tend to flower first. 

The short-styled plants have a short pistil, half the 
length of the tube of the corolla, with a smooth de- 
pressed stigma standing beneath the anthers. The 
stamens are long; the grains of pollen are spherical 
and larger. The tube of the corolla is of uniform 
diameter except close to the upper end. The number 
of seeds produced is larger. 

I have examined a large number of flowers; and 
though the shape of the stigma and the length of the 
pistil both vary, especially in the short-styled form, I 
have never met with any transitional states between 
the two forms in plants growing in a state of nature. 
There is never the slightest doubt under which form a 
plant ought to be classed. The two kinds of flowers are 


* «Nat. Hist. Review,’ July 1862, p. 237. 


18 WETEROSTYLED DIMORPHIC PLANTS. (Cuap. 1. 


never found on the same individual plant. I marked 
many Cowslips and Primroses, and on the following 
year all retained the same character, as did some in my 
garden which flowered out of their proper season in the 
autumn. Mr. W. Wooler, of Darlington, however, in- 
forms us that he has seen early blossoms on the Polyan- 
thus,* which were not long-styled, but became so later 
in the season. Possibly in this case the pistils may not 
have been fully developed during the early spring. An 
excellent proof of the permanence of the two forms may 
be seen in nursery-gardens, where choice varieties of 
the Polyanthus are propagated by division ; and I found 
whole beds of several varieties, each consisting exclu- 
sively of the one or the other form. The two forms exist 
in the wild state in about equal numbers: I collected 
522 umbels from plants growing in several stations, 
taking a single umbel from each plant; and 241 were 
long-styled, and 281 short-styled. No difference in 
tint or size could be perceived in the two great masses 
of flowers. 

We shall presently see that most of the species of 
Primula exist under two analogous forms; and it may 
be asked what is the meaning of the above-described 
important differences in their structure? The ques- 
tion seems well worthy of careful investigation, and I 
will give my observations on the cowslip in detail. 
The first idea which naturally occurred to me was, 
that this species was tending towards a dicecious 
condition; that the long-styled plants, with their 
longer pistils, rougher stigmas, and smaller pollen- 
grains, were more feminine in nature, and would pro- 
duce more seed ;—that the short-styled plants, with 
their shorter pistils, longer stamens and larger pol- 


* T have proved by numerous that the Polyanthus is a variety 
experiments, hereafter tobe given, of Primula veris. 


Cuar. I. PRIMULA VERIS. 19 


len-grains, were more masculine in nature. Accord- 
ingly, in 1860, I marked a few cowslips of both forms 
growing in my garden, and others growing in an 
open field, and others in a shady wood, and gathered 
and weighed the seed. In all the lots the short- 
styled plants yielded, contrary to my expectation, most 
seed. Taking the lots together, the following is the 


result :— 
TABLE 1. 


Number | Number | Number | Weight 

— of of Umbels of Capsules; of Seed in 

Plants. | produced. produced. | grains. 
faa ed ik Et S| ees 


: | 
Short-styled cowslips . . . 9 33 199 83 


Long-styled cowslips . . . 13 51 261 91 


If we compare the weight from an equal number of 
plants, and from an equal number of umbels, and from 
an equal number of capsules of the two forms, we get 
the following results :— 


TABLE 2. 
a2 Number of Seed Samper wet Samper Wh 
in 
Plants. grains. | ‘Umbels.| Seed. sules. went 
: 
Short-styled cowslips . 10 92 100 | 251 |} 100] 41 
Long-styled cowslips . 10 | 70 100 | 178 | 100 | 34 
. | 


So that, by all these standards of comparison, the 
short-styled form is the more fertile; if we take the 
number of umbels (which is the fairest standard, for 
large and small plants are thus equalised), the short- 
styled plants produce more seed than the long-styled, 
in the proportion of nearly four to three. 

In 1861 the trial was made in a fuller and fairer 


20 HETEROSTYLED DIMORPHIC PLANTS. OCuapr. L 


manner. A number of wild plants had been trans- 
planted during the previous autumn into a large bed 
in my garden, and all were treated alike; the result 
was— 


TABLE 3. 
Number | Number Weight 
—— 0 of of Seed in 
Plants. Umbels. grains. 
Short-styled cowslips . | 47 173) it 
Long-styled cowslips. . | 58 208 | 692 
| | 


These figures give us the following proportions :— 


TABLE 4. 
Number | Weight || Number | Weight 
——— to) of Seed in of of Seed in 
Plants. grains. Umbels. | grains. 
Short-styled cowslips . . . | 100 | 1585 | 100 | 430 
Long-styled cowslips . . 100 | 1093 100 | 332 
} | 


The season was much more favourable this year than 
the last ; the plants also now grew in good soil, instead 
of in a shady wood or struggling with other plants in 
the open field; consequently the actual produce of 
seed was considerably larger. Nevertheless we have 
the same relative result; for the short-styled plants 
produced more seed than the long-styled in nearly the 
proportion of three to two; but if we take the fairest 
standard of comparison, namely, the product of seeds 
from an equal number of umbels, the excess is, as in 
the former case, nearly as four to three. 

Looking to these trials made during two successive 
years on a large number of plants, we may safely con- 
clude that the short-styled form is more productive 
than the long-styled form, and the same result holds 


Cuar. I. PRIMULA VERIS. of 


good with some other species of Primula. Conse- 
quently my anticipation that the plants with longer 
pistils, rougher stigmas, shorter stamens and smaller 
pollen-grains, would prove to be more feminine in 
nature, is exactly the reverse of the truth. 

In 1860 a few umbels on some plants of both the 
long-styled and short-styled form, which had been 
covered by a net, did not produce any seed, though 
other umbels on the same plants, artificially fertilised, 
produced an abundance of seed; and this fact shows 
that the mere covering in itself was not injurious. 
Accordingly, in 1861, several plants were similarly 
coyered just before they expanded their flowers; these 
turned out as follows :— 


TABLE 5, 


Number | Number 
of of Umbels 
Plants. produced. 


Product of Seed. 


Pee 4 : 
Short-styled . . . Git 2A eae grain weight of seed, 
| or about 50 in number. 
| 
Long-styled . . . 18>) 74: Not one seed. 


Judging from the exposed plants which grew all round 
in the same bed, and had been treated in the same 
manner, excepting that they had been exposed to 
the visits of insects, the above six short-styled plants 
ought to have produced 92 grains’ weight of seed 
instead of only 1°3; and the eighteen long-styled 
plants, which produced not one seed, ought to have 
produced above 200 grains’ weight. The production of 
a few seeds by the short-styled plants was probably due 
to the action of Thrips or of some other minute insect. 
It is scarcely necessary to give any additional evidence, 
but I may add that ten pots of polyanthuses and 


pi HETEROSTYLED DIMORPHIC PLANTS. Cuap. I. 


cowslips of both forms, protected from insects In my 
greenhouse, did’ not set one pod, though artificially 
fertilised flowers in other pots produced an abundance. 
We thus see that the visits of insects are absolutely 
necessary for the fertilisation of Primula veris. If the 
corolla of the long-styled form had dropped off, in- 
stead of remaining attached in a withered state to 
the ovarium, the anthers attached to the lower part of 
the tube with some pollen still adhering to them 
would have been dragged over the stigma, and the 
flowers would have been partially self-fertilised, as is 
the case with Primula Sinensis through this means. 

It is a rather curious fact that so trifling a difference 
as the falling-off of the withered corolla, should make 
a very great difference in the number of seeds pro- 
duced by a plant if its flowers are not visited by 
insects. 

The flowers of the cowslip and of the other species of 
the genus secrete plenty of nectar; and I have often 
~ seen humble-bees, especially B. hortorum and muscorun, 
sucking the former in a proper manner,* though they 
sometimes bite holes through the corolla. No doubt 
moths likewise visit the flowers, as one of my sons 
caught Cucullia verbasci in the act. The pollen readily 
adheres to any thin object which is inserted into a 
flower. The anthers in the one form stand nearly, but 
not exactly, on a level with the stigma of the other; 
for the distance between the anthers and stigma in the 
short-styled form is greater than that in the long- 
styled, in the ratio of 100 to 90. This difference is 
the result of the anthers in the long-styled form 
standing rather higher in the tube than does the 
stigma in the short-styled, and this favours their 


* H. Miiller has also seen An- sucking the flowers. ‘Nature,’ 
thophora pilipes and a Bombylius Dee. 10th, 1874, p. 111. 


Cuap. I. PRIMULA VERIS. 25 


pollen being deposited on it. It follows from the 
position of the: organs that if the proboscis of a 
dead humble-bee, or a thick bristle or rough needle, 
be pushed down the corolla, first of one form and 
then of the other, as an insect would do in visiting 
the two forms growing mingled together, pollen from 
the long-stamened form adheres round the base of 
the object, and is left with certainty on the stigma 
of the long-styled form; whilst pollen from the short 
stamens of the long-styled form adheres a little way 
above the extremity of the object, and some is 
generally left on the stigma of the other form. In 
accordance with this observation I found that the 
two kinds of pollen, which could easily be recog- 
nised under the microscope, adhered in this manner 
to the proboscides of the two species of humble- 
bees and of the moth, which were caught visiting 
the flowers; but some small grains were mingled 
with the larger grains round the base of the proboscis, 
and conversely some large grains with the small 
grains near the extremity of the proboscis. Thus 
pollen will be regularly carried from the one form 
to the other, and they will reciprocally fertilise one 
another. Nevertheless an insect in withdrawing its 
proboscis from the corolla of the long-styled form 
cannot fail occasionally to leave pollen from the same 
flower on the stigma; and in this case there might 
be self-fertilisation. But this will be much more 
likely to occur with the short-styled form; for when I 
inserted a bristle or other such object into the corolla 
of this form, and had, therefore, to pass it down be- 
tween the anthers seated round the mouth of the 
corolla, some pollen was almost invariably carried 
down and left on the stigma. Minute insects, such 
as Thrips, which sometimes haunt the flowers, would 


24 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I. 


likewise be apt to cause the self-fertilisation of both 
forms. 

The several foregoing facts led me to try the effects 
of the two kinds of pollen on the stigmas of the 
two forms. Four essentially different unions are pos- 
sible; namely, the fertilisation of the stigma of the 
long-styled form by its own-form pollen, and by that 
of the short-styled; and the stigma of the short-styled 
form by its own-form pollen, and by that of the long- 
styled. The fertilisation of either form with pollen from 
the other form may be conveniently called a legitimate 
union, from reasons hereafter to be made clear ; and that 
of either form with its own-form pollen an dlegitimate 
union. I formerly applied the term “ heteromorphic ” 
to the legitimate unions, and “ homomorphic” to the 
illegitimate unions; but after discovering the exist- 
ence of trimorphic plants, in which many more unions 
are possible, these two terms ceased to be applicable. 
The illegitimate unions of both forms might have been 
tried in three ways; for a flower of either form may be 
fertilised with pollen from the same flower, or with that 
from another flower on the same plant, or with that 
from a distinct plant of the same form. But to make 


my experiments perfectly fair, and to avoid any evil © 


result from self-fertilisation or too close interbreeding, 
I have invariably employed pollen from a distinct 
plant of the same form for the illegitimate unions of 
all the species; and therefore it may be observed that 
I have used the term “ own-form pollen” in speaking 
of such unions. The several plants in all my experi- 
ments were treated in exactly the same manner, and 
were carefully protected by fine nets from the access of 
insects, excepting Thrips, which it is impossible to ex- 
clude. I performed all the manipulations myself, and 
weighed the seeds in a chemical balance; but during 


Cuar. I. PRIMULA VERIS. 25 


many subsequent trials I followed the more accurate 
plan of counting the seeds. Some of the capsules con- 
tained no seeds, or only two or three, and these are 
excluded in the column headed “good capsules” in 
several of the following tables :— 


TABLE 6. 
Primula veris. 


RAE Total | Calculated 
f | Number | Number | W eight | Weight of 
Nature of the Union. eirw ers | G of ; an oe of Seed in | Seed — 
or apsules | Capsules. ains. {| 100 goo 
fertilised. “conte i Capsules. 
Long-styled by pollen 
ofshort-styled. Le->} 22 |, 15 14 8°8 62 
gitimate union . | | | 
Long-styled by own-] | 
form pollen. Ille-| 20 | 8 5 2°1 42 
gitimate union. . 
Short-styled by pollen | 
of long-styled. Le- IB LON iy ga 2 11 4°9 44 
Ba oey, 
gitimate union. .)| 
Short-styled by own-}| 
form pollen.  Ille- 15) | 8 6 1°8 30 
P 
gitimate union. 
SUMMARY ‘ 
The two legitimate)| < ‘ 2 ; 
mise } a5.) at 25 | 13-7 | 54 
The two illegitimate)| e : . 
EEGUS: tye *} 7 = | = | a8 me 


The results may be given in another form (Table 7) 
by comparing, first, the number of capsules, whether 
good or bad, or of the good alone, produced by 100 
flowers of both forms when legitimately and illegiti- 
mately fertilised; secondly, by comparing the weight 
of seed in 100 of these capsules, whether good or bad ; ; 
or, thirdly, in 100 of the good capsules. 


26 HETEROSTYLED DIMORPHIC PLANTS. Cuar. I. 


TABLE 7. 
' 
!Numpber : 
| of |Number|Number) Weight |Number Weight |Number) Weight 
Nature of the lr owers of of good | of Seed of | of Seed || of good | of Secd 
2 


Union. fore Cap- Cap- in Cap- | in Cap- in 


| tilisea. sules. | sules. | grains. || sules. Peewee sules. | grains. 


—_—nsé—— 


54 


gitimate}/ 100| 77 | 71 39 100 | 50 100 


The two le- 
unions 


The two il- 


eg 100 | 45 31 11 100 24 | 100 35 


unions 


We here see that the long-styled flowers fertilised 
with pollen from the short-styled yield more capsules, 
especially good ones (i.e. containing more than one 
or two seeds), and that these capsules contain a greater 
proportional weight of seeds than do the flowers of the 
long-styled when fertilised with pollen from a distinct 
plant of the same form. So it is with the short-styled 
flowers, if treated in an analogous manner. Therefore I 
have called the former method of fertilisation a legiti- 
mate union, and the latter, as it fails to yield the full 
complement of capsules and seeds, an illegitimate 
union. These two kinds of union are graphically re- 
presented in Fig. 2. 

If we consider the results of the two legitimate 
unions taken together and the two illegitimate ones, 
as shown in Table 7, we see that the former com- 
pared with the latter yielded capsules, whether con- 
taining many seeds or only a few, in the proportion of 
77 to 45, or as 100 to 58. But the inferiority of the 
illegitimate unions is here perhaps too great, for on a 
subsequent occasion 100 long-styled and short-styled 
flowers were illegitimately fertilised, and they together 
yielded 53 capsules: therefore the rate of 77 to 53, or 
as 100 to 69, is a fairer one than that of 100 to 58. 


Cuap. 1. PRIMULA VERIS. 27 


Returning to Table 7, if we consider only the good 
capsules, those from the two legitimate unions were to 
those from the two illegitimate in number as 71 to 31, 
or as 100 to 44. Again, if we take an equal number of 
capsules, whether good or bad, from the legitimately 
and illegitimately fertilised flowers, we find that the 
former contained seeds by weight compared with the 
latter as 50 to 24, or as 100 to 48; but if all the 


Fig. 2. 


Legitimate union. 
Complete fertility. 


/ i 
Illegitimate / \ [legitimate 
union. | + union. 
Incomplete |! t Incomplete 
fertility. | 1 fertility. 
‘ 
4 
4 


KW} 


Legitimate union. 
Complete fertility. 


Long-styled Short-styled 
form. form. 


poor capsules are rejected, of which many were pro- 
duced by the illegitimately fertilised flowers, the propor- 
tion is 54 to 35, or as 100 to 65. In this and all other 
cases, the relative fertility of the two kinds of union 
can, I think, be judged of more truly by the average 
number of seeds per capsule than by the proportion of 
flowers which yield capsules. The two methods might 


28 HETEROSTYLED DIMORPHIC PLANTS. Cuap. L 


have been combined by giving the average number of 
seeds produced by all the flowers which were fertilised, 
whether they yielded capsules or not; but I have 
thought that it would be more instructive always to 
show separately the proportion of flowers which pro- 
duced capsules, and the average number of apparently 
good seeds which the capsules contained. 

Flowers legitimately fertilised set seeds under con- 
ditions which cause the almost complete failure of 
illegitimately fertilised flowers. Thus in the spring of 
1862 forty flowers were fertilised at the same time in 
both ways. The plants were accidentally exposed in 
the greenhouse to too hot a sun, and a large number 
of umbels perished. Some, however, remained in mo- 
derately good health, and on these there were twelve 
flowers which had been fertilised legitimately, and 
eleven which had been fertilised illegitimately. The 
twelve legitimate unions yielded seven fine capsules, 
containing on an average each 57°3 good seeds; whilst 
the eleven illegitimate unions yielded only two cap- 
sules, of which one contained 39 seeds, but so poor, 
that I do not suppose one would have germinated, and 
the other contained 17 fairly good seeds. 

From the facts now given the superiority of a legi- 
timate over an illegitimate union admits of not the 
least doubt; and we have here a case to which no 
parallel exists in the vegetable or, indeed, in the 
animal kingdom. The individual plants of the pre- 
sent species, and as we shall see of several other 
species of Primula, are divided into two sets or 
bodies, which cannot be called distinct sexes, for 
both are hermaphrodites; yet they are to a certain 
extent sexually distinct, for they require reciprocal 
union for perfect fertility. As quadrupeds are di- 
vided into two nearly equal bodies of different sexes, 


Cuar. T. PRIMULA VERIS. 29 


so here we have two bodies, approximately equal in 
number, differing in their sexual powers and related to 
each other like males and females. There are many 
hermaphrodite animals which cannot fertilise them- 
selyes, but must unite with another hermaphrodite. 
So it is with numerous plants; for the pollen is often 
mature and shed, or is mechanically protruded, before 
the flower’s own stigma is ready; and such flowers ab- 
solutely require the presence of another hermaphro- 
dite for sexual union. But with the cowslip and various 
other species of Primula there is this wide difference, 
that one individual, though it can fertilise itself im- 
perfectly, must unite with another individual for full 
fertility ; it cannot, however, unite with any other in- 
dividual in the same manner as an hermaphrodite 
plant can unite with any other one of the same species ; 
or as one snail or earth-worm can unite with any other 
hermaphrodite individual. On the contrary, an indi- 
vidual belonging to one form of the cowslip in order 
to be perfectly fertile must unite with one of the other 
form, just as a male quadruped must and can unite 
only with the female. 

I have spoken of the legitimate unions as being 
fully fertile; and I am fully justified in doing so, for 
flowers artificially fertilised in this manner yielded 
rather more seeds than plants naturally fertilised in 
a state of nature. The excess may bt attributed to 
the plants having been grown separately in good soil. 
With respect to the illegitimate unions, we shall best 
appreciate their degree of lessened fertility by the 
following facts. Giirtner estimated the sterility of the 
unions between distinct species,* in a manner which 
allows of a strict comparison with the results of the 


* *Versuche iiber die Bastarderzeugung,’ 1849, p. 216. 


30 HETEROSTYLED DIMORPHIC PLANTS. Cnar. I. 


legitimate and illegitimate unions of Primula. With 
P. veris, for every 100 seeds yielded by the two le- 
gitimate unions, only 64 were yielded by an equal 
number of good capsules from the two illegitimate 
unions. With P. Sinensis, as we shall hereafter see, 
the proportion was nearly the same—namely, as 100 
to 62. Now Gartner has shown that, on the calcula- 
tion of Verbaseum lychnitis yielding with its own pollen 
100 seeds, it yielded when fertilised by the pollen of 
V. Pheniceum 90 seeds; by the pollen of V. nigrum, 
63 seeds; by that of V. blattaria, 62 seeds. So again, 
Dianthus barbatus fertilised by the pollen of D. superbus 
yielded 81 seeds, and by the pollen of D. Japonicus 
66 seeds, relatively to the 100 seeds produced by its 
own pollen. We thus see—and the fact is highly re- 
markable—that with Primula the illegitimate unions 
relatively to the legitimate are more sterile than 
crosses between distinct species of other genera rela- 
tively to their pure unions. Mr. Scott has given* a 
still more striking illustration of the same fact: he 
crossed Primula auricula with pollen of four other 
species (P. Palinuri, viscosa, hirsuta, and vertiecillata), 
and these hybrid unions yielded a larger average 
number of seeds than did P. awricula when fertilised 
illegitimately with its own-form pollen. 

The benefit which heterostyled dimorphic plants de- 
rive from the existence of the two forms is sufficiently 
obvious, namely, the intercrossing of distinct plants 
being thus ensured.t Nothing can be better adapted 
for this end than the relative positions of the anthers 
and stigmas in the two forms, as shown in Fig. 2; but to 


* ¢ Journ. Linn. Soe. Bot., vol. fertilisation’ how greatly the off- 
viii. 1864, p. 93. spring from intercrossed plants 

+ I have shown in my work profit in height, vigour, and 
on the ‘ Effects of Cross and Self- _ fertility. 


Cuap. I. PRIMULA VERIS. 31 


this whole subject I shall reeur. No doubt pollen will 
occasionally be placed by insects or fall on the stigma 
of the same flower; and if cross-fertilisation fails, such 
self-fertilisation will be advantageous to the plant, as 
it will thus be saved from complete barrenness. But 
the advantage is not so great as might at first be 
thought, for the seedlings from illegitimate unions do 
not generally consist of both forms, but all belong to 
the parent form; they are, moreover, in some degree 
weakly in constitution, as will be shown in a future 
chapter. If, however, a flower’s own pollen should first 
be placed by insects or fall on the stigma, it by no 
means follows that cross-fertilisation will be thus pre- 
vented. It is well known that if pollen from a distinct 
species be placed on the stigma of a plant, and some 
hours afterwards its own pollen be placed on it, the 
latter will be prepotent and will quite obliterate any 
effect from the foreign pollen; and there can hardly 
be a doubt that with heterostyled dimorphic plants, 
pollen from the other form will obliterate the effects of 
pollen from the same form, even when this has been 
placed on the stigma a considerable time before. To 
test this belief, I placed on several stigmas of a long- 
styled cowslip plenty of pollen from the same plant, 
and after twenty-four hours added some from a short- 
styled dark-red polyanthus, which is a variety of the 
cowslip. From the flowers thus treated 50 seedlings 
were raised, and all these, without exception, bore 
reddish flowers ; so that the effect of pollen from the 
same form, though placed on the stigmas twenty-four 
hours previously, was quite destroyed by that of pollen 
from a plant belonging to the other form. 

Finally, I may remark that of the four kinds of 
unions, that of the short-styled illegitimately fertilised 
with its own-form pollen seems to be the most sterile of 


32 HETEROSTYLED DIMORPHIC PLANTS. Cnap. L 


all, as judged by the average number of seeds, which 
the capsules contained. A smaller proportion, also, of 
these seeds than of the others germinated, and they 
germinated more slowly. The sterility of this union is 
the more remarkable, as it has already been shown 
that the short-styled plants yield a larger number of 
seeds than the long-styled, when both forms are fer- 
tilised, either naturally or artificially, in a legitimate 
manner. 

In a future chapter, when I treat of the offspring 
from heterostyled dimorphic and trimorphic plants 
illegitimately fertilised with their own-form pollen, I 
shall have occasion to show that with the present 
species and several others, equal-styled varieties some- 
times appear. ’ 


PRIMULA ELATIOR, Jacq. 
Bardfield Oxlip of English Authors. 


This plant, as well as the last or Cowslip (P. veris, 
vel officinalis), and the Primrose (P.vulgaris, vel acaulis) 
have been considered by some botanists as varieties of 
the same species. But they are all three undoubtedly 
distinct, as will be shown in the next chapter. The 
present species resembles to a certain extent in general 
appearance the common oxlip, which is a hybrid be- 
tween the cowslip and primrose. Primula elatior is 
found in England only in two or three of the eastern 
counties ; and I was supplied with living plants by Mr. 
Doubleday, who, as I believe, first called attention to 
its existence in England. It is common in some parts 
of the Continent; and H. Miiller* has seen several 
kinds of humble-bees and other bees, and Bombylius, 
visiting the flowers in North Germany. 


* “Die Befruchtung der Blumen,’ p. 347. 


Cuar. I. PRIMULA ELATIOR. oo 


The results of my trials on the relative fertility of 
the two forms, when legitimately and illegitimately 
fertilised, are given in the following table :— 


TABLE 8. 


Primula elatior. 


Number Number | Maximum] Minimum | Average 
N f Uni of of good | of Seeds | of Seeds | Number of 
ature of Union. Flowers Capsules |in any one]in any one; Seeds per 
| fertilised. produced.| Capsule. | Capsule. | Capsule. 
Tongeutylod fermi; by 
pollen of short- =styled. 10 6 62 34 | 46°5 
ee union | 
Long-sty ey ten, form, by 
own-form pollen. 20 + 49* 2 27°7 
legitimate union. pail 
Short-styled form, by Sevier, by)| 
pollen of long- styled. 61 Te REY 
Legitimate union (eon) aee 
Short-styled form, by 
own-form pollen. Bey £7 ie 9 12°1 
legitimate union. pagey 
“The two legitimate 20 62 37 | 47-41 
unions together : 
The two illegitimate Sadie stant) | > x 
unions together . 4 vil > ae 


* These seeds were so poor and small that they could hardly have germinated. 


If we compare the fertility of the two legitimate 
unions taken together with that of the two illegitimate 
unions together, as judged by the proportional number 
of flowers which when fertilised in the two methods 
yielded capsules, the ratio is as 100 to 27; so that by 
this standard the present species is much more sterile 
than P. veris, when both species are illegitimately fer- 
tilised. If we judge of the relative fertility of the two 
kinds of unions by the average number of seeds per 
capsule, the ratio is as 100 to 75. But this latter 


34 HETEROSTYLED DIMORPHIC PLANTS. Guar. I. 


number is probably much too high, as many of the seeds 
produced by the illegitimately fertilised long-styled 
flowers were so small that they probably would not 
have germinated, and ought not to have been counted. 
Several long-styled and short-styled plants were pro- 
tected from the access of insects, and must have been 
spontaneously self-fertilised. They yielded altogether 
only six capsules, containing any seeds; and their 
average number was only 7°8 per capsule. Some, 
moreover, of these seeds were so small that they could 
hardly have germinated. 

Herr W. Breitenbach informs me that he examined, 
in two sites near the Lippe (a tributary of the Rhine), 
894 flowers produced by 198 plants of this species; and 
he found 467 of these flowers to be long-styled, 411 
short-styled, and 16 equal-styled. I have heard of no 
other instance with heterostyled plants of equal-styled 
flowers appearing in a state of nature, though far from 
rare with plants which have been long cultivated. It 
is still more remarkable that in eighteen cases the 
same plant produced both long-styled and short-styled, 
or long-styled and equal-styled flowers; and in two 
out of the eighteen cases, long-styled, short-styled, and 
equal-styled flowers. The long-styled flowers greatly 
preponderated on these eighteen plants,—61 consisting 
of this form, 15 of equal-styled, and 9 of the short- 
styled form. 


PRIMULA VULGARIS (var. acaulis, Linn.), 
The Primrose of English Writers. 


Mr. J. Scott examined 100 plants growing near 
Edinburgh, and found 44 to be long-styled, and 56 
short-styled; and I took by chance 79 plants in Kent, 
of which 39 were long-styled and 40 short-styled; so 


——_— 


Cuar. I. PRIMULA VULGARIS. 35 


that the two lots together consisted of 83 long-styled 
and 96 short-styled plants. In the long-styled form 
the pistil is to that of the short-styled in length, from 
an average of five measurements, as 100 to 51. The 
stigma in the long-styled form is conspicuously more 
globose and much more papillose than in the short- 
styled, in which latter it is depressed on the summit ; 


Fig. 3. 


Outlines of pollen-gwains of Primula vulyaris, distended with water, much 
magnified and drawn under the camera lucida, The upper and smaller 
grains from the long-styled form; the lower and larger grains from 
the short-styled. 


it is equally broad in the two forms. In both it stands 
nearly, but not exactly, on a level with the anthers of 
the opposite form; for it was found, from an average 
of 15 measurements, that the distance between the 
middle of the stigma and the middle of the anthers 
in the short-styled form is to that in the long-styled 
as 100 to 95. The anthers do not differ in size in the 
two forms. The pollen-grains from the short-styled 


36 HETEROSTYLED DIMORPHIC PLANTS. Cnuap. I. 


flowers before they were soaked in water were decidedly 
broader, in proportion to their length, than those from 
the long-styled ; after being soaked they were relatively 
to those from the long-styled as 100 to 71 in diameter, 
and more transparent. A large number of flowers from 
the two forms were compared, and 12 of the finest 
flowers from each lot were measured, but there was no 
sensible difference between them in size. Nine long- 
styled and eight short-styled plants growing together in 
a state of nature were marked, and their capsules col- 
lected after they had been naturally fertilised ; and 
the seeds from the short-styled weighed exactly twice 
as much as those from an equal number of long-styled 
plants. So that the primrose resembles the cowslip in 
the short-styled plants, being the more productive of 
the two forms. The results of my trials on the fer- 
tility of the two forms, when legitimately and illegi- 
timately fertilised, are given in Table 9. 

We may infer from this table that the fertility of the 
two legitimate unions taken together is to that of the 
two illegitimate unions together, as judged by the pro- 
portional number of flowers which when fertilised in 
the two methods yielded capsules, as 100 to 60. If we 
judge by the average number of seeds per capsule pro- — 
duced by the two kinds of unions, the ratio is as 100 
to 54; but this latter figure is perhaps rather too low. 
It is surprising how rarely insects can be seen during the 
day visiting the flowers, but I have occasionally observed 
small kinds of bees at work ; I suppose, therefore, that 
they are commonly fertilised by nocturnal Lepidoptera. 
The long-styled plants when protected from insects 
yield a considerable number of capsules, and they thus 
differ remarkably from the same form of the cowslip, 
which is quite sterile under the same circumstances. 
‘Twenty-three spontaneously self-fertilised capsules from 


Cuar. I. PRIMULA VULGARIS. oF 


TABLE 9. 


Primula vulgaris. 


+ Maximum | Minimum 
; ase sine aE Number | Number Holtaee 
seiee of Puion. Flowers Capsules eee Se cape Seeds per 
fertilised. produced. Capbaile. Gans Capsule. 
Long-styled form, by pol- 
len from short-styled. 12 11 77 47 66°9 
Legitimate union, . 
Long-styled form, by 
own-form pollen. Il-)) 21 14 66 30 52°2 
legitimate union . | 
ee eal d et S 
Short-styled form, by}! L 
pollen from long-style d. 8 i! 75 48 65°0 
Legitimate union , 
Short-styled form, by 
own-form pollen. II- 18 ii 43 5 18°8* 
legitimate union . 
The __ two legitimate), 20 18 a 47 66-0 
unions together “Ji | 
The two illegitimate) 39 1 66 5 35°5* 
unions together 
| 


* This average is perhaps rather too low. 


this form contained, on an average, 19-2 seeds. The 
short-styled plants produced fewer spontaneously self- 
fertilised capsules, and fourteen of them contained only 
6-2 seeds per capsule. The self-fertilisation of both forms 
was probably aided by Thrips, which abounded within 
the flowers; but these minute insects could not have 
placed nearly sufficient pollen on the stigmas, as the 
spontaneously self-fertilised capsules contained much 
fewer seeds, on an average, than those (as may be seen 
in Table 9) which were artificially fertilised with their 
own-form pollen. But this difference may perhaps be 
attributed in part to the flowers in the table having 
been fertilised with pollen from a distinct plant be- 


38 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I. 


longing to the same form; whilst those which were 
spontaneously self-fertilised no doubt generally received 
their own pollen. In a future part of this volume sonie 
observations will be given on the fertility of a red- 
coloured variety of the primrose. 


PRIMULA SINENSIS. 


In the long-styled form the pistil is about twice as 
long as that of the short-styled, and the stamens differ 
in a corresponding, but reversed, manner. ' The stigma 
is considerably more elongated and rougher than that 
of the short-styled, which is smooth and almost 
spherical, being somewhat depressed on the summit; 
but the stigma varies much in all its characters, the 
result, probably, of cultivation. The pollen-grains of 
the short-styled form, according to Hildebrand,* are 
7 divisions of the micrometer in length and 5 in 
breadth; whereas those of the long-styled are only 
4 in length and 3 in breadth. The grains, there- 
fore, of the short-styled are to those of the long- 
styled in length as 100 to 57. Hildebrand also re- 
marked, as I had done in the case of P. veris, that the 
smaller grains from the long-styled are much more 
transparent than the larger ones from the short-styled 
form. We shall hereafter see that this cultivated 
plant varies much in its dimorphic condition and is 
often equal-styled. Some individuals may be said to 
be sub-heterostyled ; thus in two white-flowered plants 
the pistil projected above the stamens, but in one of them 


* After the appearance of my 
paper this author published some 
excellent observations on the 
present species (‘ Bot. Zeitung,’ 
Jan. 1, 1864), and he shows 


that I erred greatly about the 
size of the pollen-grains in the 
two forms. I suppose that by 
mistake I measured twice over 
pollen-grains from the same form. 


‘Ouar. L PRIMULA SINENSIS. 39 


it was longer and had a more elongated and rougher 
stigma, than in the other; and the pollen-grains from 
the latter were to those from the plant with a more 
elongated pistil only as 100 to 88 in diameter, instead 
of as 100 to 57. The corolla of the long-styled and 
short-styled form differs in shape, in the same manner 
as in P. veris. The long-styled plants tend to flower 
before the short-styled. When both forms were legiti- 
mately fertilised, the capsules from the short-styled 
plants contained, on an average, more seeds than those 
from the long-styled, in the ratio of 12:2 to 9:3 by 
weight, that is, as 100 to 78. In the following table 
we have the results of two sets of experiments tried 
at different periods. 
TABLE 10. 


Primula Sinensis. 


[| 2? | 


H P Average Number 
| Aunler N pole eae of Seeds per 
: } Co) of goo! eight of | 6 as 
Nature of Union. | Flowers | Capsules Seeds per eee Be a 
- fertilised. produced, | Capsule. subsequent 
| occasion. 
Long-styled form, by eee siel Ginn, by pollen) | | 
of short-styled. Saas 24 16 0°58 50 « 
mate union . 
Long-styled fxm, by own- 
form pollen. iy 20 13 0°45 35 
mate union , 
Short- PR iad form, by pol-) form, by pol- | 
len of agian Le- 8 8 0-76 | 64 
lS ae union , 
(Bhoré-styiea form, by own-] -styled form, by own- 
form pollen. rice 7 4 O-23. 91 25 
mate union. . 
The two legitimate unions 
together . sae 32 24 | 0°64 57 
The two illegitimate unions ; | | 
Brae 7) 27 | 17 | 0°40 | 30 


40 HETEROSTYLED DIMORPHIC PLANTS. Cuap. L 


The fertility, therefore, of the two legitimate unions 
together to that of the two illegitimate unions, as judged 
by the proportional number of flowers which yielded 
capsules, is as 100 to 84. Judging by the average 
weight of seeds per capsule produced by the two kinds 
of unions, the ratio is as 100 to 63. On another ocea- 
sion a large number of flowers of both forms were 
fertilised in the same manner, but no account of their 
number was kept. The seeds, however, were carefully 
counted, and the averages are shown in the right-hand 
column. The ratio for the number of seeds produced 
by the two legitimate compared with the two illegiti- 
mate unions is kere 100 to 53, which is probably more 
accurate than the foregoing one of 100 to 63. 

Hildebrand in the paper above referred to gives the 
results of his experiments on the present species; and 
these are shown in a condensed form in the following 
table (11). Besides using for the illegitimate unions 
pollen from a distinct plant of the same form, as was 
always done by me, he tried, in addition, the effects of - 
the plant’s own pollen. He counted the seeds. 

It is remarkable that here all the flowers which 
were fertilised legitimately, as well as those fertilised 
illegitimately with pollen from a distinct plant be- 
longing to the same form, yielded capsules ; and from 
this fact it might be inferred that the two forms were 
reciprocally much more fertile in his case than in 
mine. But his illegitimately fertilised capsules from 
both forms contained fewer seeds relatively to the 
legitimately fertilised capsules than in my experi- 
ments; for the ratio in his case is as 42 to 100, 
instead of, as in mine, as 53 to 100. Fertility is a 
very variable element with most plants, being deter- 
mined by the conditions to which they are subjected, of 
which fact I have observed striking instances with the 


Cuap. I. PRIMULA SINENSIS. 41 


TABLE 11. 
Primula Sinensis (from Hildebrand). 


Number | Number | Average 
of of good |Number of 

Flowers | Capsules | Seeds per 

fertilised. | produced. | Capsule. 


Nature of Union. 


Long-styled form, by pollen of short- 14 | 14 | 41 
styled. Legitimate union. . site | 
Long-styled form, by own-form pollen, from 2% | 96 | 18 
a distinct plant. Illegitimate union .f| ~ 
Long-styled form, by pollen from same 97 21 17 
flower. Illegitimate union. . : ‘i 
Short-styled form, by pollen of paee 
styled. Legitimate union . “S| @ | — = 
‘Short. styled form, by own-form pollen, 16 16 | 20 
from a distinct plant. Illegitimate union 
Short-styled, by pollen from the same}\| 21 7 8 
flower. Illegitimate union. | ra | 
The two legitimate unions together 28! vad || 228 43 
“The two illegitimate unions together)! : | 
(own-form pollen) =. ee } = = | ue 
| ee 
The two illegitimate unions together (pol-)| | 
len from the same flower) , i) = e _ 
| ' 


present species; and this may account for the differ- 
ence between my results and those of Hildebrand. His 
plants were kept in a room, and perhaps were grown in 
too small pots or under some other unfavourable condi- 
tions, for his capsules in almost every case contained a 
smaller number of seeds than mine, as may be seen 
by comparing the right-hand columns in Tables 10 
and 11. © 

The most interesting point in Hildebrand’s experi- 
ments is the difference in the effects of illegitimate 
fertilisation with a flower’s own pollen, and with that 


42 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I. 


from a distinct plant of the same form. In the latter 
case all the flowers produced capsules, whilst only 67 
out of 100 of those fertilised with their own pollen pro- 
duced capsules. ‘The self-fertilised capsules also con- 
tained seeds, as compared with capsules from flowers 
fertilised with pollen from a distinct plant of the same 
form, in the ratio of 72 to 100. 

In order to ascertain how far the present species was 
spontaneously self-fertile, five long-styled plants were 
protected by me from insects; and they bore up to a 
given period 147 flowers which set 62 capsules; but 
many of these soon fell off, showing that they had not 
been properly fertilised. At the same time five short- 
styled plants were similarly treated, and they bore 116 
flowers which ultimately produced only seven capsules. 
On another occasion 13 protected long-styled plants 
yielded by weight 25°9 grains of spontaneously self- 
fertilised seeds. At the same time seven protected 
short-styled plants yielded only half-a-grain weight of 
seeds. Therefore the long-styled plants yielded nearly 
24 times as many spontaneously self-fertilised seeds as 
did the same number of short-styled plants. The chief 
cause of this great difference appears to be, that when 
the corolla of a long-styled plant falls off, the anthers, 
from being situated near the bottom of the tube are 
necessarily dragged over the stigma and leave pollen 
on it, as I saw when I hastened the fall of nearly 
withered flowers; whereas in the short-styled flowers, 
the stamens are seated at the mouth of the corolla, 
and in falling off do not brush over the lowly-seated 
stigmas. Hildebrand likewise protected some long- 
styled and short-styled plants, but neither ever yielded 
a single capsule. He thinks that the difference in our 
results may be accounted for by his plants haying 
been kept in a room and never having been shaken; 


Cuap. I. PRIMULA AURICULA. 43 


but this explanation seems to me doubtful ; bis plants 
were in a less fertile condition than mine, as shown by 
the difference in the number of seeds produced, and 
it is highly probable that their lessened fertility would 
have interfered with especial force with their capacity 
for producing self-fertilised seeds. 


PRIMULA AURIOCULA.* 


This species is heterostyled, like the preceding ones; but 
amongst the varieties distributed by florists the long-styled form 
is rare, as it is not valued. There is a much greater relative in- 
equality in the length of the pistil and stamens in the two forms 
of the auricula than in the cowslip; the pistil in the long-styled 
being nearly four times as long as that in the short-styled, in 
which itis barely longer than the ovarium. The stigma is nearly 
of the same shape in both forms, but is rougher in the long-styled, 
though the difference is not so great as between the two forms 
of the cowslip. In the long-styled plants the stamens are very 
short, rising but little above the ovarium. The pollen-grains of 
these short stamens, when distended with water, were barely;255 
of an inch in diameter, whereas those from the long stamens of 
the short-styled plants were barely ;255, showing a relative dif- 
ference of about 71 to 100. The smaller grains of the long- 
styled plant are also much more transparent, and before disten- 
tion with water more triangular in outline than those of the 
other form. Mr. Scott t compared ten plants of both forms grow- 
ing under similar conditions, and found that, although the long- 
styled plant produced more umbels and more capsules than the 
short-styled, yet they yielded fewer seeds, in the ratio of 66 to 
100. Three short-styled plants were protected by me from the 


* According to Kerner our gar- 
den auriculas are descended fromP. 
ubescens, Jacq., which is a hybrid 
etween the true P. auricula and 
hirsuta. This hybrid has now been 
propagated for about 300 years, 
and produces, when legitimately 
fertilised, a large number of seeds ; 
the long-styled forms yielding an 
average number of 73, and the 


short-styled 98 seeds per capsule: 
see his “ Geschichte der Aurikel,” 
‘ Zeitschr. des Deutschen und Oest. 
Alpen-Vereins, Band vi. p. 52. 
Also ‘ Die Primulaceen-Bastarten,’ 
‘ Oest. Bot. Zeitschrift,’ 1835, Nos. 
3, 4, and 5. 

+ ‘Journ. Linn. Soc. Bot.’ vol. 
viii. 1864, p. 86. 


44 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I. 


access of insects, and they did not produce a single seed. Mr. 
Scott protected six plants of both forms, and found them ex- 
cessively sterile. The pistil of the long-styled form stands so 
high above the anthers, that it is scarcely possible that pollen 
should reach the stigma without some aid; and one of Mr. 
Scott’s long-styled plants which yielded a few seeds (only 18 in 
number) was infested by aphides, and he does not doubt that 
these had imperfectly fertilised it. 

I tried a few experiments by reciprocally fertilising the two 
forms in the same manner as before, but my plants were un- 
healthy, so I will give, in a condensed form, the results of Mr. 
Scott’s experiments. For fuller particulars with respect to this 
and the five following species, the paper lately referred to may 
be consulted. In each ease the fertility of the two legitimate 
unions, taken together, is compared with that of the two ille- 
gitimate unions together, by the same two standards as before, 
namely, by the proportional number of flowers which pro- 
duced good capsules, and by the average number of seeds per 
capsule. The fertility of the legitimate unions is always taken 
at 100. 

By the first standard, the fertility of the two legitimate unions 
of the auricula is to that of the two illegitimate unions as 100 
to 80; and by the second standard as 100 to 15. 


PRIMULA SIKKIMENSIS. 


According to Mr. Scott, the pistil of the long-styled form is 
fully four times as long as that of the short-styled, but their 
stigmas are nearly alike in shape and roughness. The stamens 
do not differ so much in relative length as the pistils. The pollen- 
grains differ in a marked manner in the two forms; “those of 
the long-styled plants are sharply triquetrous, smaller, and more 
transparent than those of the short-styled, which are of a bluntly 
triangular form.” ‘The fertility of the two legitimate unions to 
that of the two illegitimate unions is by the first standard as 
100 to 95, and by the second standard as 100 to 31. 


PRIMULA CORTUSOIDES. 


The pistil of the long-styled form is about thrice as long as 
that of the short-styled, the stigma being double as long and 
covered with much longer papillz. The pollen-grains of the short- 


Cuar. I. SUMMARY ON PRIMULA. 45 


styled form are, as usual, “larger, less transparent, and more 
bluntly triangular than those from the long-styled plants.” The 
fertility of the two legitimate unions to that of the two ille- 
gitimate unions is by the first standard as 100 to 74, and by 
the second standard as 100 to 66. 


PRIMULA INVOLUCRATA. 


The pistil of the long-styled form is about thrice as long as 
that of the short-styled; the stigma of the former is globular 
and closely beset with papille, whilst that of the short-styled 
is smooth and depressed on the apex. The pollen-grains of the 
two forms differ in size and transparency as before, but not in 
shape. The fertility of the two legitimate to that of the two 
illegitimate unions is by the first standard as 100 to 72; and by 
the second standard as 100 to 47. 


PRIMULA FARINOSA. 


According to Mr. Scott, the pistil of the long-styled form is 
only about twice as long as that of the short-styled. The 
stigmas of the two forms differ but little in shape. The pollen- 
grains differ in the usual manner in size, but not in form. The 
fertility of the two legitimate to that of the two illegitimate 
unions is by the first standard as 100 to 71, and by the second 
standard as 10Q to 44. 


Summary on the foregoing heterostyled species of Pri- 
mula.—The fertility of the long and short-styled plants 
of the above species of Primula, when the two forms 
are fertilised legitimately, and illegitimately with 
pollen of the same form taken from a distinct plant, 
has now been given. ‘The results are seen in the fol- 
lowing table; the fertility being judged by two 
standards, namely, by that of the proportional number 
of flowers which yielded capsules, and by that of the 
average number of seeds per capsule. Bunt for full 
accuracy many more observations, under varied condi- 
tions, would be requisite. 


46 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I. 


TABLE 12. 


Summary on the Fertility of the two Legitimate Unions, compared 
with that of the two Illegitimate Unions, in the genus Primula. 
The former taken at 100. 


Illegitimate Unions. 


Judged of by the 
Average Number (or 
Weight in some cases) 
of Seeds per Capsule, 


Name of Species. Judged of by the 
Proportional Number 
of Flowers which 
produced Capsules. 


Erimulasveris apace ue ie 69 | 65 
oe: - (Probably 
Pr sClALL OTIS eae aes co. coe de 27 T+ too high.) 
‘ (Perhaps 
P. Wulgaris; 2) Ve) sti ss ee te 60 5a too low.) 
PP OINENSISs te Ove Risk” homens as 84 
35 (second trial) . . ty 53 
A: (after Hildebrand) . 100 42 
P. auricula (Scott) . . . « 80 15 
P. Sikkimensis (Scott) . . . 95 31 
P. cortusoides (Scott) . . . V4: 66 
P. involucrata (Scott) . . . 72 48 
P. farinosa (Scott) . . . - 71 ct 
Average of the nine species . | 88°4 bese Gk ae 


With plants of all kinds some flowers generally fail 
to produce capsules, from various accidental causes ; 
but this source of error has been eliminated, as far as 
possible, in all the previous cases, by the manner in 
which the calculations have been made. Supposing, 
for instance, that 20 flowers were fertilised legiti- 
mately and yielded 18 capsules, and that 30 flowers 
were fertilised illegitimately and yielded 15 cap- 
sules, we may assume that on an average an equal 
proportion of the flowers in both lots would fail to 
produce capsules from various accidental causes ; and 
the ratio of 38 to 43, or as 100 to 56 (in whole 


_ Cnap. L SUMMARY ON PRIMULA. 47 


numbers), would show the proportional number of cap- 
sules due to the two methods of fertilisation ; and the 
number 56 would appear in the left-hand column of 
Table 12, and in my other tables. With respect 
to the average number of seeds per capsule hardly 
anything need be said: supposing that the legiti- 
mately fertilised capsules contained, on an average, 
50 seeds, and the illegitimately fertilised capsules 
25 seeds; then as 50 is to 25 so is 100 to 50; and 
the latter number would appear in the right-hand 
column. 

It is impossible to look at the above table and doubt 
that the legitimate unions between the two forms of the 
above nine species of Primula are much more fertile 
than the illegitimate unions; although in the latter 
ease pollen was always taken from a distinct plant of 
the same form. There is, however, no close corre- 
spondence in the two rows of figures, which give, 
according to the two standards, the difference of fer- 
tility between the legitimate and illegitimate unions. 
Thus all the flowers of P. Sinensis which were illegiti- 
mately fertilised by Hildebrand produced capsules ; 
but these contained only 42 per cent. of the number 
of seeds yielded by the legitimately fertilised capsules. 
So again, 95 per cent. of the illegitimately fertilised 
flowers of P. Sikkimensis produced capsules ; but these 
contained only 51 per cent. of the number of seeds in 
the legitimate capsules. On the other hand, with 
P. elatior only 27 per cent. of the illegitimately fer- 
tilised flowers yielded capsules; but these contained 
nearly 75 per cent. of the legitimate number of seeds. 
It appears that the setting of the flowers, that is, the 
production of capsules whether good or bad, is not 
so much influenced by legitimate and illegitimate fer- 
tilisation as is the number of seeds which the capsules 


48 HETEROSTYLED DIMORPHIC PLANTS. Cuar. IL. 


contain. For, as may be seen at the bottom of Table 
12, 88:4 per cent. of the illegitimately fertilised 
flowers yielded capsules; but these contained only 
61°8 per cent. of seeds, in comparison, in each case, 
with the legitimately fertilised flowers and capsules 
of the same species. 
There is another point which deserves notice, 
namely, the relative degree of infertility in the several 
species of the long-styled and short-styled flowers, 
when both are illegitimately fertilised. The data 
may be found in the earlier tables, and in those given 
by Mr. Scott in the Paper already referred to. If we 
call the number of seeds per capsule produced by the 
illegitimately fertilised long-styled flowers 100, the 
seeds from the illegitimately fertilised short-styled 
flowers will be represented by the following num- 
bers :— 


Primula veris. 71 Primula auricula. . . 119 
: (Probably | P.Sikkimensis . . . 57 
LT AN auf too low.) P. cortusoides . . . 93 
- (Perhaps BP, ANVOlUCKAta = |e unsieRiee 

P. vulgaris. 364 too low.) PB. farinosa | )2)\_.! 1% Bemmape 


P. Sinensis . 71 


We thus see that, with the exception of P. auricula, the 
long-styled flowers of all nine species are more fertile 
than the short-styled flowers, when both forms are 
illegitimately fertilised. Whether P. auricula really 
differs from the other species in this respect I can form 
no opinion, as the result may have been accidental. 
The degree of self-fertility of a plant depends on two 
elements, namely, on the stigma receiving its own pollen 
and on its more or less efficient action when placed 
there. Now as the anthers of the short-styled flowers of 
several species of Primula stand directly above the 
stigma, their pollen is more likely to fall on it, or to 
be carried down to it by insects, than in the case of 


Cuap. I. HOMOSTYLED PRIMULAS. 49 


the long-styled form. It appears probable, therefore, 
at first sight, that the lessened capacity of the short- 
styled flowers to be fertilised with their own pollen, is 
a special adaptation for counteracting their greater 
liability to receive their own pollen, and thus for 
checking self-fertilisation. But from facts with respect. 
to other species hereafter to be given, this view can 
hardly be admitted. In accordance with the above 
liability, When some of the species of Primula were 
allowed to fertilise themselves spontaneously under 
a net, all insects being excluded, except such minute 
ones as Thrips, the short-styled flowers, notwith- 
standing their greater mnate self-sterility, yielded 
more seed than did the long-styled. None of the 
species, however, when insects were excluded, made 
a near approach to full fertility. But the long-styled 
form of P. Sinensis gave, under these circumstances, 
a considerable number of seeds, as the corolla in falling 
off drags the anthers, which are seated low down in 
the tube, over the stigma, and thus leaves plenty of 
pollen on it. 

Homostyled species of Primula—It has now been 
shown that nine of the species in this genus exist under 
two forms, which differ not only in structure but in 
function. Besides these Mr. Scott enumerates 27 other 
species* which are heterostyled ; and to these probably 
others will be hereafter added. Nevertheless, some 
species are homostyled; that is, they exist only under 
a single form; but much caution is necessary on this 
head, as several species when cultivated are apt to 
become equal-styled. Mr. Scott believes that P. 
Scotica, verticillata, a variety of Stbirica, elata, mollis, and 


* H. Miiller has givenin‘Na- viz. the Alpine P. villosa, and 
ture,’ Dec. 10, 1874, p. 110, a~ shows that it is fertilised exclu 
drawing of one of these species, sively by Lepidoptera. 


50 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I, 


longiflora,* are truly homostyled ; and to these may be 
added, according to Axell, P. stricta. Mz. Scott ex- 
perimented on P. Scotica, mollis, and verticillata, and 
found that their flowers yielded an abundance of seeds 
when fertilised with their own pollen. ‘This shows 
that they are not heterostyled in function. 2. Scotica 
is, however, only moderately fertile when insects are 
excluded, but this depends merely on the coherent 
pollen not readily falling on the stigma without their 
aid. Mr. Scott also found that the capsules of P. 
verticillata contained rather more seed when the flowers 
were fertilised with pollen from a distinct plant than 
when with their own pollen; and from this fact he in- 
fers that they are sub-heterostyled in function, though 
not in structure. But there is no evidence that two 
sets of individuals exist, which differ slightly in func- 
tion and are adapted for reciprocal fertilisation ; and 
this is the essence of heterostylism. The mere fact 
of a plant being more fertile with pollen from a 
distinct individual than with its own pollen, is com- 
mon to very many species, as I have shown in my 
work ‘On the Effects of Cross and Self-fertilisation.’ 


HorroniA PALUSTRIS. 


This aquatic member of the Primulacez is con- 
spicuously heterostyled, as the pistil of the long-styled 
form projects far out of the flower, the stamens being 
enclosed within the tube; whilst the stamens of the 
short-styled flower project far outwards, the pistil being 
enclosed. This difference between the two forms has 
attracted the attention of various botanists, and that 


* Koch was aware that this . Sprengel und Darwin,” ‘ Bot. Zei« 
species was homostyled: see“ Tre- tung,’ Jan, 2, 1863, p. 4. 
yiranus iiber Dichogamie nach 


* 
a 


ee Se ae ee 


ee 


Cuar. I. HOTTONIA PALUSTRIS. 51 


of Sprengel,* in 1793, who, with his usual sagacity, 
adds that he does not believe the existence of the two 
forms to be accidental, though he cannot explain their 
purpose. The pistil of the long-styled form is more 
than twice as long as that of the short-styled, with the 
stigma rather smaller, though rougher. H. Millert 
gives figures of the stigmatic papillz of the two forms, 
and those of the long-styled are seen to be more than 
double the length, and much thicker than the papille 
of the short-styled form. The anthers in the one form 
do not stand exactly on a level with the stigma in 
the other form; for the distance between the organs is 
greater in the short-styled than in the long-styled 
flowers in the proportion of 100 to 71. In dried speci- 
mens soaked in water the anthers of the short-styled 
form are larger than those of the long-styled, in the 
ratio of 100 to 83. The pollen-grains, also, from the 
short-styled flowers are conspicuously larger than those 
from the long-styled ; the ratio between the diameters 
of the moistened grains being as 100 to 64, according 
to my measurements, but according to the measure- 
ments of H. Miller as 100 to 61; and his are probably 
- the more. accurate of the two. The contents of the 
larger pollen-grains appear more coarsely granular 
and of a browner tint, than those in the smaller 
grains. The two forms of Hottonia thus agree closely 
in most respects with those of the heterostyled species 
of Primula. The flowers of Hottonia are cross-fertilised, 
according to Miller, chiefly by Diptera. 

Mr. Scott made a few trials on a short-styled plant, 
and found that the legitimate unions were in all ways 
more fertile than the illegitimate ; but since the pub- 


* ‘Das entdeckte Geheimniss t ‘Journ. Linn. Soc. Bot.’ vol. 
der Nature,’ p. 103. viil. 1864, p. 79. 
7 ‘Die Befruchtung,’ &., p.350. 


02 


HETEROSTYLED DIMORPHIC PLANTS. 


Cuap. I. 


lication of his paper H. Miller has made much fuller 
experiments, and I give his results in the following 
table, drawn up in accordance with my usual plan :— 


TABLE 13. 
Hottonia palustris (from H. Miller). 


Nature of Union. 


Long-styled form, by pollen of pias 


Legitimate union. . . 


distinct plant. 


Short-styled form, by aCe of Siete 


Legitimate union . 


Short-styled form, by own-form pollen, from a)| 


distinct plant. 


Illegitimate union . 


Long-styled form, by own-form pollen, from sack 18 


Illegitimate union . 


The two legitimate unions together 


The two illegitimate unions together . 


The most remarkable point in this table is the 
small average number of seeds from the short-styled 
flowers when illegitimately fertilised, and the unusually 
large average number of seeds yielded by the illegiti- © 
mately fertilised long-styled flowers, relatively in both 
cases to the product of the legitimately fertilised 
The two legitimate unions compared with 


flowers.* 


S Average 
N umber Number of 
of Capsules Seeds per 
examined. rp 
| 
34 91°4 
17° 
| 30 66°2 
19 18°7 | 
| | 
64 78°8 . 
; 37 48-1 


* II. Miiller says (‘Die Be- 
fruchtung,’ &c., p. 352) that the 
‘long-styled flowers, when illegiti- 
mately fertilised, yield as many 
seeds as when legitimately fer- 
tilised; but by adding up the 
number of seeds from all the cap- 
sules produced by the two methods 
of fertilisation, as given by him, 


I arrive at the results shown in 
Table 13. The average number 
in the long-styled capsules, when , 
legitimately fertilised, is 91:4, 

and when illegitimately fertilised, 

77°5; oras 100 to 85. H. Miiller 
agrees with me that this is the 
proper manner of viewing the 
case. 


Cuap. I. ANDROSACE. 58 


the two illegitimate together yield seeds in the ratio 
of 100 to 61. 

H. Miller also tried the effects of illegitimately fer- 
tilising the long-styled and short-styled flowers with 
their own pollen, instead of with that from another 
plant of the same form; and the results are very 
striking. For the capsules from the long-styled 
flowers thus treated contained, on an average, only 
15:7 seeds instead of 77:5; and those from the 
short-styled 6°5, instead of 18-7 seeds per capsule. 
The number 6°5 agrees closely with Mr. Scott’s result 
from the same form similarly fertilised. 

From some observations by Dr. Torrey, Hottonia 
inflata, an inhabitant of the United States, does not 
appear to be heterostyled, but is remarkable from pro- 
ducing cleistegamic flowers, as will be seen in the last 
chapter of this volume. 

Besides the genera Primula and Hottonia, Androsace 
(vel Gregoria, vel Aretia) vitalliana is heterostyled. 
Mr. Scott* fertilised with their own pollen 21 flowers 
on three short-styled plants in the Edinburgh Botanic 
Gardens, and not.one yielded a single seed; but 
eight of them which were fertilised with pollen from one 
of the other plants of the same form, set two empty 
capsules. He was able to examine only dried speci- 
mens of the long-styled forms. But the evidence seems 
sufficient to leave hardly a doubt that Androsace is 
heterostyled. Fritz Miller sent me from South Brazil 
dried flowers of a Statice which he believed to be hete- 
rostyled. In the one form the pistil was considerably 
longer and the stamens slightly shorter than the cor- 
responding organs in the other form. But as in the 
shorter-styled form the stigmas reached upto the anthers 


* See also Treviranus in ‘ Bot. Zeitung,’ 1863, p. 6, on this plant 
being dimorphic. 


54 HETEROSTYLED DIMORPHIC PLANTS. Cuap. L 


of the same flower, and as I could not detect in the 
dried specimens of the two forms any difference in their 
stigmas, or in the size of their pollen-grains, I dare not 
rank this plant as heterostyled. From statements made 
by Vaucher I was led to think that Soldanella alpina was 
heterostyled, but it is impossible that Kerner, who has 
closely studied this plant, could have overlooked the 
fact. So again from other statements it appeared prob- 
able that Pyrola might be heterostyled, but H. Miller 
examined for me two species in North Germany, and 
found this not to be the case. 


Cuap. II. HYBRID PRIMULAS. 59 


CHAPTER IL. 


Hyprip PRIMULAS. 


The Oxlip a hybrid naturally produced between Primula veris and 
yulgaris—The differences in structure and function between the 
two parent-species—Effects of crossing long-styled and short-styled 
Oxlips with one another and with the two forms of both parent- 
species—Character of the offspring from Oxlips artificially self- 
fertilised and cross-fertilised in a state of nature—Primula elatior 
shown to be a distinct species—Hybrids between other heterostyled 
species of Primula—Supplementary note on spontaneously produced 
hybrids in the genus Verbascum. 


THE various species of Primula have produced in a 
state of nature throughout Europe an extraordinary 
number of hybrid forms. For instance, Proféssor 
Kerner has found no less than twenty-five such forms 
in the Alps.* The frequent occurrence of hybrids in 
this genus no doubt has been favoured by most of the 
species being heterostyled, and consequently requiring 
cross-fertilisation by insects; yet in some other genera, 
species which are not heterostyled and which in some 
respects appear not well adapted for hybrid-ferti- 
lisation, have likewise been largely hybridised. In 
certain districts of England, the common oxlip—a 
hybrid between the cowslip (P. veris, vel officinalis) 
and the primrose (P. vulgaris, vel acaulis)—is fre- 
quently found, and it occurs occasionally almost every- 


* “Tie Primulaceen-Bastarten,’ ‘Bull. Soc. Bot. de France,’ tom. x. 
‘Oesterr. Bot. Zeitschrift,” Jahr 1853, p. 178. Also in ‘ Revue des 
1875, Nos. 3,4, and 5. See also Sciences Nat.’ 1875, p. 331. 
Godron on hybrid Primulas in 


56 HYBRID PRIMULAS. Cuap. II. 


where. Owing to the frequency of this intermediate 
hybrid form, and to the existence of the Bardfield 
oxlip (P. elatior), which resembles to a certain extent 
the common oxlip, the claim of the three forms to 
rank as distinct species has been discussed oftener 
and at greater length than that of almost any other 
plant. Linneus considered P. veris, vulgaris and 
elatior to be varieties of the same species, as do some 
distinguished botanists at the present day; whilst 
others who have carefully studied these plants do not 
doubt that they are distinct species. The following 
observations prove, I think, that the latter view is 
correct ; and they further show that the common oxlip 
is a hybrid between P. veris and vulgaris. 

The cowslip differs so conspicuously in general ap- 
pearance from the primrose, that nothing need here 
be said with respect to their external characters.* 
But some less obvious differences deserve notice. As 
both species are heterostyled, their complete fertili- 
sation depends on insects. The cowslip is habitually 
visited during the day by the larger humble-bees 
(viz. Bombus muscorum and hortorwm), and at night 
by moths, as I have seen in the case of Cucullia. The 
primrose is never visited (and I speak after many 
years’ observation) by the larger humble-bees, and 
only rarely by the smaller kinds; hence its ferti- 
lisation must depend almost exclusively on moths. 
There is nothing in the structure of the flowers of the 
two plants which can determine the visits of such 
widely different insects. But they emit a different 
odour, and perhaps their nectar may have a different 
taste. Both the long-styled and short-styled forms of 


* The Rev. W. A. Leighton seed, in ‘Ann. and Mag. of Nat. 
has pointed outcertain differences Hist.’ 2nd series, vol. ii. 1848, 
in the form of the capsules and pp. 164. 


Cuar. IL. THE COMMON OXLIP. aT 


the primrose, when legitimately and-naturally ferti- 
lised, yield on an average many more seeds per capsule 
than the cowslip, n namely) in the proportion of 100 to 55. 
When illegitimately fertilised they are likewise more 
fertile than the two forms of the cowslip, as shown by 
the larger proportion of their flowers which set cap- 
sules, and by the larger average number of seeds which 
the capsules contain. The difference also between the 
number of seeds produced by the long-styled and short- 
styled flowers of the primrose, when both are illegiti- 
mately fertilised, is greater than that between the 
number produced under similar circumstances by the 
two forms of the cowslip. The long-styled flowers of 
the primrose when protected from the access of all in- 
sects, except such minute ones as Thrips, yield a con- 
siderable number of capsules containing on an average 
19-2 seeds per capsule ; whereas 18 plants of the long- 
styled cowslip similarly treated did not yield a single 
seed. 

The primrose, as every one knows, flowers a little 
earlier in the spring than the cowslip, and inhabits 
slightly different stations and districts. The primrose 
generally grows on banks or in woods, whilst the cow- 
slip is found in more open places. The geographical 
range of the two forms is different. Dr. Bromfield re- 
marks * that “the primrose is absent from all the in- 
terior region of northern Europe, where the cowslip is 
indigenous.” In Norway, however, both plants range 
to the same degree of north latitude.t 

The cowslip and primrose, when intercrossed, be- 


* *Phytologist,’ vol. iii. p. 694. centre de la France,’ 1840, tom. ii. 
t H. Lecoq, *Géograph. Bot.de —_p. 376. With respect to the rarity 
Europe,’ tom. viii. 1858, pp.141, of P. veris in western Scotland, 
144. See also ‘Ann. and Mag. of see H.C. Watson, ‘ Cybele Britan- 
Nat. Hist.’ ix. 1842, pp. 1 56, nica,’ it p. 293: 
515. Also Boreau, i Flore du 


rn 


58 HYBRID PRIMULAS. Cuap. II. 


have’ like distinct species, for they are far from 
being mutually fertile. Gartner* crossed 27 flowers 
of P. vulgaris with pollen of P. veris, and obtained 
16 capsules; but these did not contain any good 
seed. He also crossed 21 flowers of P. veris with 


pollen of P. vulgaris; and now he got only five’ 


capsules, containing seed in a still less perfect 
condition. Gartner knew nothing about hetero- 
stylism; and his complete failure may perhaps be 
accounted for by his having crossed together the 
same forms of the cowslip and primrose; for such 
crosses would have been of an illegitimate as well as 
of a hybrid nature, and this would have increased 
their sterility. My trials were rather more fortunate. 
Twenty-one flowers, consisting of both forms of the 
cowslip and primrose, were intercrossed legitimately, 
and yielded seven capsules (¢.e. 83 per cent.), contain- 
ing on an average 42 seeds; some of these seeds, 
however, were so poor that they probably would not have 
germinated. ‘Twenty-one flowers on the same cowslip 
and primrose plants were also intercrossed illegiti- 
mately, and they likewise yielded seven capsules (or 
33 per cent.), but these contained on an average only 
13 good and bad seeds. I should, however, state that 
some of the above flowers of the primrose were fertilised 
with pollen from the polyanthus, which is certainly a 
- variety of the cowslip, as may be inferred from the per- 
fect fertility inter se of the crossed offspring from these 
two plants.t ‘To show how sterile these hybrid unions 


* ‘ Bastarderzeugung, 1849, p. ciently numerous. ‘The degree of 


“721. 

+ Mr. Scott has discussed the 
nature of the polyanthus (‘ Proc. 
Linn. Soe.’ viii. Bot. 1864, p. 
103), and arrives at a different 
conclusion; but I do not think 
that his experiments were suffi- 


infertility of a cross is liable to 
much fluctuation. Pollen from 
the cowslip at first appears rather 
more efficient on the primrose than 
that of the polyanthus; for 12 
flowers of both forms of the prim- 
rose, fertilised legitimately and 


Cuap. II. THE COMMON OXLIP. 59 


were I may remind the reader that 90 per cent. of the 
flowers of the primrose fertilised legitimately with 
primrose-pollen yielded capsules, containing on an 
average 66 seeds; and that 54 per cent. of the flowers 
fertilised illegitimately yielded capsules containing on 
an average 30°5 seeds per capsule. The primrose, 
especially the short-styled form, when fertilised by the 
cowslip, is less sterile, as Gartner likewise observed, 

than is the cowslip when fertilised by the primrose. The 
above experiments also show that a cross between the. 
same forms of the primrose and cowslip is much more 
sterile than that between different forms of these two 
species. ; 

The seeds from the several foregoing crosses were 
sown, but none germinated except those from the 
short-styled primrose fertilised with pollen of the 
polyanthus; and these seeds were the finest of the 
whole lot. I thus raised six plants, and compared 
them with a group of wild oxlips which I had trans- 
planted into my garden. One of these wild oxlips 
produced slightly larger flowers than the others, and 
this one was identical in every character (in foliage, 
flower-peduncle, and flowers) with my six plants, 
excepting that the flowers of the latter were tinged of 
a dingy red colour, from being descended from the 
polyanthus. 

We thus see that the cowslip and primrose can- 
not be crossed either way except with considerable 
difficulty, that they differ conspicuously in external 
appearance, that they differ in various physiological 


illegitimately with pollen of the 
cowslip gave five capsules, contain- 
ing on an average 32:4 seeds, 


22°6 seeds. On the other hand, 
the seeds produced by the poly- 
anthus- pollen were much the 


whilst 18 flowers similarly fertil- 
ised by polyantlius-pollen yielded 
only five capsules, containing only 


finest of the whole lot, and were 
the only ones which germinated. 


60 HYBRID PRIMULAS. Cuap. IL. 


characters, that they inhabit slightly different stations 
and range differently. Hence those botanists who 
rank these plants as varieties ought to be able to prove 
that they are not as well fixed in character as are most 
species ; and the evidence in favour of such instability 
of character appears at first sight very strong. It 
rests, first, on statements made by several competent 
observers that they have raised cowslips, primroses, and 
oxlips from seeds of the same plant; and, secondly, 
on the frequent occurrence in a state of nature of 
plants presenting every intermediate gradation between 
the cowslip and primrose. 

The first statement, however, is of little value; 
for, heterostylism not being formerly understood, 
the seed-bearing plants were in no instance* pro- 
tected from the visits of insects; and there would 
be almost as much risk of an isolated cowslip, or of 
several cowslips if consisting of the same form, being 
crossed by a neighbouring primrose and producing 
oxlips, as of one sex of a dicecious plant, under similar 
circumstances, being crossed by the opposite sex of 
an allied and neighbouring species. Mr. H. C. Wat- 
son, a critical and most careful observer, made many 
experiments by sowing the seeds of cowslips and of 


various kinds of oxlips, and arrived at the following 


conclusion,t namely, “that seeds of a cowslip can 
produce cowslips and oxlips, and that seeds of an oxlip 
can produce cowslips, oxlips, and primroses.” This 
conclusion harmonises perfectly with the view that in 


* One author states in the ¢ Pliy- 
tologist’ (vol. iii. p. 703) that he 
coyceredwith bell-glasses some cow- 
slips, primroses, &e , on which he 
experimented. He specifies all 
tiie details of his experiment, but 
does not say that he artificially 
fertilised his plants; yet he ob- 


tainel an abundance of seed, 
which is simply impossible. 
Hence there must have been 
some strange error in these ex- 
periments, which may be passed 
over as valueless, 

t ‘Phytologist? ii. pp. 217, 
852; ili. p. 43. * 


Cuap. II. THE COMMON OXLIP. 61 


all eases, when such results have been obtained, the 
unprotected cowslips have been crossed by primroses, 
and the unprotected oxlips by either cowslips or 
primroses ; for in this latter case we might expect, by 
the aid of reversion, which notoriously comes into 
powerful action with hybrids, that the two parent-forms 
in appearance pure, as well as many intermediate gra- 
dations, would be occasionally produced. Nevertheless 
the two following statements offer considerable diffi- 
culty. The Rey. Prof. Henslow* raised from seeds of a 
cowslip growing in his garden, various kinds of oxlips 
and one perfect primrose; but a statement in the same 
paper perhaps throws light on this anomalous result. 
Prof. Henslow had previously transplanted into his 
garden a cowslip, which completely changed its ap- 
pearance during the following year, and now resembled 
an oxlip. Next year again it changed its character, 
and produced, in addition to the ordinary umbels, a 
few single-flowered scapes, bearing flowers somewhat 
smaller and more deeply coloured than those of the 
common primrose. From what Ihave myself observed 
with oxlips, I cannot doubt that this plant was an ox- 
lip in a highly variable condition, almost like that of 
the famous Cytisus adami. This presumed oxlip was 
propagated by offsets, which were planted in different 
parts of the garden; and if Prof. Henslow took by 
mistake seeds from one of these plants, especially if it 
had been crossed by a primrose, the result would be 
quite intelligible. Another case is still more difficult 
to understand: Dr. Herbertt raised, from the seeds of 
a highly cultivated red cowslip, cowslips, oxlips of 
yarious kinds, and a primrose. ‘This case, if accurately 


* Loudon’s ‘ Mag. of Nat. Hist.’ iii. 1830, p. 409. 
t ‘Transact. Hort. Soc.’ iv. p. 19. 


62 HYBRID PRIMULAS. Cuap. II. 


recorded, which I much doubt, is explicable only on 
the improbable assumption that the red cowslip was 
not of pure parentage. With species and varieties 
of many kinds, when intercrossed, one is sometimes 
strongly prepotent over the other; and instances are 
known* of a variety crossed by another, producing 
offspring which in certain characters, as in colour, 
hairiness, &c., haye proved identical with the pollen- 
bearing parent, and quite dissimilar to the mother- 
plant; but I do not know of any instance of the off- 
spring of a cross perfectly resembling, in a consider- 
able number of important characters, the father alone. 
It is, therefore, very improbable that a pure cowslip 
crossed by a primrose should ever produce a primrose 
in appearance pure. Although the facts given by Dr. 
Herbert and Prof. Henslow are difficult to explain, yet 
until it can be shown that a cowslip ora primrose, 
carefully protected from insects, will give birth to at 
least oxlips, the cases hitherto recorded have little 
weight in leading us to admit that the cowslip and 
primrose are varieties of one and the same species. 
Negative evidence is of little value; but the follow- 
ing facts may be worth giving :—Some cowslips which 
had been transplanted from the fields into a shrubbery 
were again transplanted into highly manured land. 
In the following year they were protected from insects, 
artificially fertilised, and the seed thus procured was 
sown ina hotbed. The young plants were afterwards 
planted out, some in very rich soil, some in stiff poor 
clay, some in old peat, and some in pots in the green- 
house ; so that these plants, 765 in number, as well as 
their parents, were subjected to diversified and un- 


* T have given instances in my  tication,’ chap, xv. 2nd edit. vol. 
work ‘On the Variation of Ani- ii. p. 69. 
mals and Plants under Domes- 


Cap. II. THE COMMON OXLIP. 63 


natural treatment; but not one of them presented the 
least variation except in size—those in the peat at- 
taining almost gigantic dimensions, and those in the 
clay being much dwarfed. 

I do not, of course, doubt that cowslips exposed 
during several successive generations to changed con- 
ditions would vary, and that this might occasionally 
occur in a state of nature. Moreover, from the law 
of analogical variation, the varieties of any one species 
of Primula would probably in some cases resemble 
other species of the genus. For instance I raised a red 
primrose from seed from a protected plant, and the 
flowers, though still resembling those of the primrose, 
were borne during one season in umbels on a long foot- 
stalk like that of a cowslip. 

With regard to the second class of facts in support 
of the cowslip and primrose being ranked as mere 
varieties, namely, the well-ascertained existence in a 
state of nature of numerous linking forms* :—If it can 
be shown that the common wild oxlip, which is inter- 
mediate in character between the cowslip and prim- 
rose, resembles in sterility and other essential respects 
a hybrid plant, and if it can further be shown that the 
oxlip, though in a high degree sterile, can be fertilised 
by either parent-species, thus giving rise to still finer 
gradational links, then the presence of such linking 
forms in a state of nature ceases to be an argument 
of any weight in favour of the cowslip and primrose 
being varieties, and becomes, in fact, an argument on 
the other side. The hybrid origin of a plant in a 
state of nature can be recognised by four tests: first, 
by its occurrence only where both presumed parent- 


* See an excellent article on in the ‘ Phytologist, vol. iii. p, 
this subject by Mr. H. C. Watson 43. 


a 


64 HYBRID PRIMULAS. Caapr. II. 


species exist or have recently existed ; and this holds 
good, as far as I can discover, with the oxlip; but the 
P. elatior of Jacq., which, as we shall presently see, 
constitutes a distinct species, must not be confounded 
with the common oxlip. Secondly, by the supposed 
hybrid plant being nearly intermediate in character 
between the two parent-species, and especially by its 
resembling hybrids artificially made between the same 
two species. Now the oxlip is intermediate in cha- 
racter, and resembles in every respect, except in the 
colour of the corolla, hybrids artificially produced be- 
tween the primrose and the polyanthus, which latter 
is a variety of the cowslip. Thirdly, by the supposed 
hybrids being more or less sterile when crossed tnter se: 
but to try this fairly two distinct plants of the same 
parentage, and not two flowers on the same plant, 
should be crossed; for many pure species are more 
or less sterile with pollen from the same individual 
plant ; and in the case of hybrids from heterostyled 
species the opposite forms should be crossed. Fourthly 
and lastly, by the supposed hybrids being much more 
fertile when crossed with either pure parent-species 
than when crossed dnter se, but still not as fully fertile 
as the parent-species. 

For the sake of ascertaining the two latter points, 
I transplanted a group of wild oxlips into my 
garden. They consisted of one long-styled and 
three short-styled plants, which, except in the co- 
rolla of one being slightly larger, resembled each 
other closely. The trials which were made, and the 
results obtained, are shown in the five following 
tables. No less than twenty different crosses are 
necessary in order to ascertain fully the fertility of 
hybrid heterostyled plants, both inter se and with 
their two parent-species. In this instance 256 flowers 


_ al 


Cuar. II. THE COMMON OXLIP. 65 


were crossed in the course of four seasons. I may 
mention, as a mere curiosity, that if any one were to 
raise hybrids between two trimorphic heterostyled 
species, he would have to make 90 distinct unions 
in order to ascertain their fertility in all ways; 
and as he would have to try at least 10 flowers in 
each case, he would be compelled to fertilise 900 
flowers and count their seeds. This would probably 
exhaust the patience of the most patient man. 


TABLE 14. 


’ Crosses inter se between the two forms of the common Ozlip. 


Mlegitimate union. | Legitimate union. Illegitimate union. | Legitimate union. 


Short-styled ox-| Short-styled ox- Long-styled ox-| Long-styled ox- 
lip, by pollen of lip, by pollen of lip, by its own/lip, by pollen of 
short-styled oxlip:|long-styled oxlip: pollen: 24 flowers | short-styled oxlip: 
20 flowers fertilised, |10flowers fertilised, fertilised, produced | 10 flowers fertilised, 
did not produce one did not produce one five capsules, con- | did not produce one 
capsule. | capsule. taining 6, 10, 20, ‘capsule. 

| 8, and 14 seeds, 
Average 11°6 


TABLE 15. 


Both forms of the Oxlip crossed with Pollen of both forms of the 
Cowslip, P. veris. 


Illegitimate union. | Legitimate union. | Illegitimate union. | Legitimate union. 


Short-styled ox-| Short-styled ox-| Long -styled ox | Long - styled ox- 
lip, by pollen of|lip, by pollen of lip, by pollen of lip, by pollen of 
short-styled cow-|long-styled cow-| long - styled cow- | short ~ styled cow- 
slip: 18 flowers fer-| slip: 18 flowers | ‘slip: 11 flowers |slip: 5 flowers 
tilised, did not pro-| fertilised, produced | fertilised, produced | fertilised, produced 
duce one capsule. | three capsules, con-| one capsule, con- | two capsules, con- 

taining 7, 3, and 3 taining 13 wretched taining 21 and 28 
wretched seeds, ap-| seeds, | very tine seeds. 
parently incapable | 
of germination. 

| 


eee 


66 HYBRID PRIMULAS. Cuap. 11. 


TABLE 16. 


Both forms of the Oxlip crossed with Poilen of both forms of the 
Primrose, P. vulgaris. 


Illegitimate union. | Legitimate union. | Illegitimate union. | Legitimate union. 


Short-styled ox-| Short-styled ox-| Long-styled ox-| Long-styled ox- 
lip, by pollen of}lip, by pollen of lip, by pollen of|lip, by pollen of 
short-styled prim-}long-styled prim- long-styled prim-|short-styled prim- 
rose: 34 flowers!rose: 26 flowers|rose: 11 flowers|rose: 5 flowers 
fertilised, produced | fertilised, produced | fertilised, produced | fertilised, produced 
two capsules, con-| six capsules, con- ‘four capsules, con-| five capsules, con- 
taining 5 and 12) taining 16, 20,5, 10,| taining 10, 7,5, and | taining 26, 32, 23, 
seeds. | 19, and 24 seeds. 6 wretched seeds. | 28, and 34 seeds. 

| Average 15°7. Many Average 7°0. Average 28°6. 
‘of the seeds very 
poor, some good. 


TABLE 17. 
Both forms of the Cowslip crossed with Pollen of both forms of the Oxlip. 


{ | 
Illegitimate union. | Legitimate union. | [legitimate union. | Legitimate union. 


Short-styled cow-| Long-styled cow- _ Long-styled cow-| Short-styled cow- 
slip, by pollen ofjslip, by pollen of slip, by pollen of) slip, by pollen of 
short-styled oxlip:|short-styled oxlip: long-styled oxlip:|long-styled oxlip: 
8 flowers fertilised, 8 flowers fertilised, 8 flowers fertilised, | 8 flowers fertilised, 
produced not one) produced one cap- produced three cap-| produced eight cap- 


capsule. sule, containing 26 sules, containing 5, | sules, containing 58, 
| seeds. 6, and 14 seeds.|38, 31, 44, 23, 26, 
| Average 8:3. 37, and 66 seeds. 


Average 40°4. 


TABLE 18. 
Both forms of the Primrose crossed with Pollen of both forms of the Oxlip. 


| 
Illegitimate union. | Legitimate union. | Illegitimate union. | Legitimate union. 


Short-styledprim-| Long-styled prim- | Long-styled prim- Short-styled prim- 
rose, by pollen of rose, by pollen of rose, by pollen of rose, by pollen of 
short-styled oxlip:short-styled oxlip; long-styled oxlip:|long-styled oxlip: 
8 flowers fertilised, 8 flowers fertilised, 8 flowers fertilised, | 8 flowers fertilised, 
produced not one produced two cap- | _ produced eight cap-| produced four cap- 


capsule. |sules, containing 5 sules,containing 15,|sules, containing 
| and 2 seeds. | 7, 12, 20, 22, 7,16, | 52, 52, 42, and 49 

) and 13 seeds. Ave-| seeds,some good and 

(Tage 14:0. some bad. Average 


| 48°7. 


ee a 


Cuar. II. THE COMMON OXLIP. 67 


We see in these five tables the number of capsules 
and of seeds produced, by crossing both forms of the 
oxlip in a legitimate and illegitimate manner with one 
another, and with the two forms of the primrose and 
cowslip. I may premise that the pollen of two of the 
short-styled oxlips consisted of nothing but minute 
aborted whitish cells; but in the third short-styled 
plant about one-fifth of the grains appeared in a sound 
condition. Hence it is not surprising that neither 
the short-styled nor the long-styled oxlip produced a 
single seed when fertilised with this pollen. Nor did 
the pure cowslips or primroses when illegitimately fer- 
tilised with it; but when thus legitimately fertilised 
' they yielded a few good seeds. The female organs of 
the short-styled oxlips, though greatly deteriorated in 
power, were in a rather better condition than the male 
organs; for though the short-styled oxlips yielded no 
seed when fertilised by the long-styled oxlips, and 
hardly any when illegitimately fertilised by pure cow- 
slips or primroses, yet when legitimately fertilised by 
these latter species, especially by the long-styled 
primrose, they yielded a moderate supply of good 
seed. 

The long-styled oxlip was more fertile than the 
three short-styled oxlips, and about half its pollen- 
grains appeared sound. It bore no seed when legiti- 
mately fertilised by the short-styled oxlips; but this 
no doubt was due to the badness of the pollen of 
the latter; for when illegitimately fertilised (Table 
14) by its own pollen it produced some good seeds, 
though much fewer than self-fertilised cowslips or 
primroses would have produced. The long-styled ox- 
lip likewise yielded a very low average of seed, as may 
be seen in the third compartment of the four latter 
tables, when illegitimately fertilised by, and when 


68 . HYBRID PRIMULAS. Cuar. IL. 


illegitimately fertilising, pure cowslips and primroses. 
The four corresponding legitimate unions, however, were 
moderately fertile, and one (viz. that between a short- 
styled cowslip and the long-styled oxlip in Table 17) 
was nearly as fertile as if both parents had been pure. 
A short-styled primrose legitimately fertilised by the 
long-styled oxlip (‘Table 18) also yielded a moderately 
good average, namely 48°7 seeds; but if this short- 
styled primrose had been fertilised by a long-styled 
primrose it would have yielded an average of 65 seeds. 
If we take the ten legitimate unions together, and the 
ten illegitimate unidns together, we shall find that 29 
per cent. of the flowers fertilised in a legitimate manner 
yielded capsules, these containing on an average 27°4 
good and bad seeds; whilst only 15 per cent. of the 
flowers fertilised in an illegitimate manner yielded 
capsules, these containing on an average only 11:°0 
good and bad seeds. 

In a previous part of this chapter it was shown that 
illegitimate crosses between the long-styled form of 
the primrose and the long-styled cowslip, and between 
the short-styled primrose and short-styled cowslip, are 
mere sterile than legitimate crosses between these two 
species; and we now see that the same rule holds good 
almost invariably with their hybrid offspring, whether — 
these are crossed inter se, or with either parent-species ; 
so that in this particular case, but not as we shall pre- 
sently see in other cases, the same rule prevails with 
the pure unions between the two forms of the same 
heterostyled species, with crosses between two distinct 
heterostyled species, and with their hybrid offspring. 

Seeds from the long-styled oxlip fertilised by its 
own pollen were sown, and three long-styled plants 
raised. The first of these was identical in every 
character with its parent. The second bore rather 


Cuap. IT. THE COMMON OXLIP. 69 


smaller flowers, of a paler colour, almost like those of 
the primrose; the scapes were at first single-flowered, 
but later in the season a tall thick scape, bearing many 
flowers, like that of the parent oxlip, was thrown up. 
The third plant likewise produced at first only single- 
flowered scapes, with the flowers rather small and of a 
darker yellow; but it perished early. The second 
plant also died in September; and the first plant, 
though all three grew under very favourable con- 
ditions, looked very sickly. Hence we may infer that 
seedlings from self-fertilised oxlips would hardly be 
able to exist in a state of nature. I was surprised to 
find that all the pollen-grains in the first of these seed- 
ling oxlips appeared sound; and in the second only a 
moderate number were bad. These two plants, however, 
had not the power of producing a proper number of 
seeds; for though left uncovered and surrounded by 
pure primroses and cowslips, the capsules were esti- 
mated to include an average of only from fifteen to 
twenty seeds. 

From having many experiments in hand, I did not 
sow the seed obtained by crossing both forms of the 
primrose and cowslip with both forms of the oxlip, 
which I now regret; but I ascertained an interest- 
ing point, namely, the character of the offspring 
from oxlips growing in a state of nature near both 
primroses and cowslips. The -oxlips were the same 
plants which, after their seeds had been collected, were 
transplanted and experimented on. From the seeds 
thus obtained eight plants were raised, which, when 
they flowered, might have been mistaken for pure 
primroses ; but on close comparison the eye in the 
centre of the corolla was seen to be of a darker yellow, 
and the peduncles more elongated.. As the season ad- 
vanced, one of these plants threw up two naked scapes, 


70 HYBRID PRIMULAS. Cuapr. IL 


-7 inches in height, which bore umbels of flowers of 
the same character as before. This fact led me to ex- 
amine the other plants after they had flowered and 
were dug ‘up; and I found that the flower-peduncles 
of all sprung from an extremely short common scape, 
of which no trace can be found in the pure primrose. 
Hence these plants are beautifully intermediate be- 
tween the oxlip and the primrose, inclining rather 
towards the latter ; and we may safely conclude that the 
parent oxlips had been fertilised by the surrounding 
primroses. 

From the various facts now given, there can be no 
doubt that the common oxlip is a hybrid between the 
cowslip (P. verts, Brit. Fl.) and the primrose (P. vul- 
garis, Brit. Fl.), as has been surmised by several 
botanists. It is probable that oxlips may be produced 
either from the cowslip or the primrose as the seed- 
bearer, but oftenest from the latter, as I judge from 
the nature of the stations in which oxlips are generally 
found,* and from the primrose when crossed by the 
cowslip being more fertile than, conversely, the cowslip 
by the primrose. The hybrids themselves.are also 
rather more fertile when crossed with the primrose 
than with the cowslip. Whichever may be the seed- 
bearing plant, the cross is probably between different 
forms of the two species ; for we have seen that legiti- 
mate hybrid unions are more fertile than illegitimate 
hybrid unions. Moreover a friend in Surrey found 
that 29 oxlips which grew in the neighbourhood of 
his house consisted of 13 long-styled and 16 short- 
styled plants; now, if the parent-plants had been 
illegitimately united, either the long- or short-styled 
form would have greatly preponderated, as we shall 

* See also on this head Hardwicke’s ‘Science Gossip, 1867, pp, 
114, 137. 


i a _ 


— ee ee 


Cuap. II. THE COMMON OXLIP. ral 


hereafter see good reason to believe. The case of 
the oxlip is interesting; for hardly any other in- 
stance is known of a hybrid spontaneously arising 
in such large numbers over so wide an extent of coun- 
try. The common oxlip (not the P. elatior of Jacq.) 
is found almost everywhere throughout England, where 
both cowslips and primroses grow. In some districts, 
as I have seen near Hartfield in Sussex and in parts 
of Surrey, specimens may be found on the borders of 
almost every field and small wood. In other districts 
the oxlip is comparatively rare: near my own resi- 
dence I have found, during the last twenty-five years, 
not more than five or six plants or groups of plants. 
It is difficult to conjecture what is the cause of this 
difference in their number. It is almost necessary 
that a plant, or several plants belonging to the same 
form, of one parent-species, should grow near the 
opposite form of the other parent-species; and it is 
further necessary that both species should be fre- 
quented by the same kind of insect, no doubt a moth. 
The cause of the rare appearance of the oxlip in 
certain districts may be the rarity of some moth, 
which in other districts habitually visits both the 
primrose and cowslip. 

Finally, as the cowslip and primrose differ in the 
various characters above specified,—as they are in a 
high degree sterile when intercrossed,—as there is no 
trustworthy evidence that either species, when un- 
crossed, has ever given birth to the other species or 
to any intermediate form,—and as the intermediate 
forms which are often found in a state of nature have 
been shown to be more or less sterile hybrids of the 
first or second generation,—we must for the future 
look at the cowslip and primrose as good and true 
species. 


T2 THE BARDFIELD OXLIP. Cuar. IL. 


Primula elatior, Jacq., or the Bardfield Oxlip, is 
found in England only in two or three of the eastern 
counties. On the Continent it has a somewhat dif- 
ferent range from that of the cowslip and primrose ; 
and it inhabits some districts where neither.of these 
species live.* In general appearance it differs so 
much from the common oxlip, that no one accustomed 
to see both forms in the living state could afterwards 
confound them; but there is scarcely more than a 
‘single character by which they can be distinetly de- 
fined, namely, their linear-oblong capsules equalling 
the calyx in length.f The capsules when mature differ 
conspicuously, owing to their length, from those of the 
cowslip and primrose. With respect to the fertility 
of the two forms when these are united in the four 
possible methods, they behave like the other hetero- 
styled species of the genus, but differ somewhat (see 
Tables 8 and 12) in the smaller proportion of the il- 
legitimately fertilised flowers which set capsules. That 
P. elatior is not a hybrid is certain, for when the two 
forms were legitimately united they yielded the large 
average of 47°1 seeds, and when illegitimately united 
30°5 per capsule ; whereas, of the four possible unions 
(Table 14) between the two forms of the common ox- 
lip which we know to be a hybrid, one alone yielded 
any seed; and in this case the average number was 
only 11:6 per capsule. Moreover I could not detect 
a single bad pollen-grain in the anthers of the short- 
styled P. elatior ; whilst in two short-styled plants of 
the common oxlip all the grains were bad, as were 
a large majority in a third plant. As the common 


* For England, see Hewett C. 1858, p, 142. For the Alps, see 
Watson, ‘Cybele Britannica, vol. ‘Ann. and Mag. Nat. Hist.’ vol. 
ii, 1849, p. 292. For the Con- ix. 1842, pp. 156 and 515. 
tinent, see Lecoq, ‘ Géograph. + Babington’s ‘ Manual of Brit- 
Botanique de ’ Europe, tom. viii. ish Botany,’ 1851, p. 258. 


Cuar. I. THE BARDFIELD OXLIP. 13 


oxlip is a hybrid between the primrose and cowslip, it 
is not surprising that eight long-styled flowers of the 
primrose, fertilised by pollen from the long-styled 
common oxlip, produced eight capsules (Table 18), 
containing, however, only a low average of seeds; 
whilst the same number of flowers of the primrose, 
similarly fertilised by the long-styled Bardfield oxlip, 
produced only a single capsule; this latter plant 
being an altogether distinct species from the primrose. 
Plants of P. elatior have been propagated by seed in 
a garden for twenty-five years, and have kept all this 
time quite constant, excepting that in some cases the 
flowers varied a little in size and tint.* Nevertheless, 
according to Mr. H. C. Watson and Dr. Bromfield,t 
plants may be occasionally found in a state of nature, 
in which most of the characters by which this species 
can be distinguished from P. veris and vulgaris fail ; 
but such intermediate forms are probably due to 
hybridisation ; for Kerner states, in the paper before 
referred to, that hybrids sometimes, though rarely, 
arise in the Alps between P. elatior and veris. 

Finally, although we may freely admit that Primula 
veris, vulgaris, and elatior,as well as all the other 
species of the genus, are descended from a common 


primordial form, yet from the facts above given, we 


must conclude that these three forms are now as fixed 
in character as are many others which are universally 
ranked as true species. Consequently they have as 
good a right to receive distinct specific names as have, 
for instance, the ass, quagga, and zebra. 


Mr. Scott has arrived at some interesting results by 


* See Mr. H. Doubleday in the __ p. 462. 
*Gardener’s Chronicle, 1867, p. t ‘ Phytologist,’ vol. i. p. 1001, 
435, also Mr. W. Marshall, ibid. and vol. iii. p. 695. 


74 HYBRID PRIMULAS. Cuar. IL. 


crossing other heterostyled species of Primula.* I 
have already alluded to his statement, that in four 
instances (not to mention others) a species when crossed 
with a distinct one yielded a larger number of seeds 
than the same species fertilised illegitimately with its 
own-form pollen, though taken from a distinct plant. 
It has long been known from the researches of Kélreuter 
and Gartner, that two species when crossed reciprocally 
sometimes differ as widely as is possible in their fer- 
tility : thus A when crossed with the pollen of B will 
yield a large number of seeds, whilst B may be crossed 
repeatedly with pollen of A, and will never yield a single 
seed. Now Mr. Scott shows in several cases that the 
same law holds good when two heterostyled species 
of Primula are intercrossed, or when one is crossed 
with a homostyled species. But the results are much 
more complicated than with ordinary plants, as two 
heterostyled dimorphic species can be intercrossed in 
eight different ways. I will give one instance from 
Mr. Scott. The long-styled P. hirsuta fertilised legi- 
timately and illegitimately with pollen from the two 
forms of P. auricula, and reciprocally the long-styled 
P. auricula fertilised legitimately and illegitimately 
with pollen from the two forms of P. hirsuta, did 
not produce a single seed. Nor did the short- 
styled P. hirsuta when fertilised legitimately and 
illegitimately with the pollen of the two forms of 
P. auricula. On the other hand, the short-styled 
P. auricula fertilised with pollen from the long-styled 
P. hirsuta yielded capsules containing on an average 
no less than 56 seeds; and the short-styled P. 
auricula by pollen of the short-styled P. hirsuta 
yielded capsules containing on an average 42 seeds 


* ¢ Journ. Linn, Soc. Bot.’ vol. viii. 1864, p. 93 to end. 


Ouar. IL. HYBRID VERBASCUMS. 75 


per capsule. So that out of the eight possible unions 
between the two forms of these two species, six 
were utterly barren, and two fairly fertile. We have 
seen also the same sort of extraordinary irregularity in 
the results of my twenty different crosses (Tables 
14 to 18), between the two forms of the oxlip, prim- 
rose, and cowslip. Mr. Scott remarks, with respect 
to the results of his trials, that they are very surprising, 
as they show us that “the sexual forms of a species 
manifest in their respective powers for conjunction 
with those of another species, physiological peculiari- 
ties which might well entitle them, by the criterion of 
fertility, to specifie distinction.” 

Finally, although P. veris and vulgaris, when crossed 
legitimately, and especially when their hybrid offspring 
are crossed in this manner with both parent-species, 
were decidedly more fertile, than when crossed in an 
illegitimate manner, and although the legitimate cross 
effected by Mr. Scott between P. auricula and hirsuta 
was more fertile, in the ratio of 56 to 42, than the 
illegitimate cross, nevertheless it is very doubtful, 
from the extreme irregularity of the results in the 
various other hybrid crosses made by Mr. Scott, whether 
it can be predicted that two heterostyled species are 
generally more fertile if crossed legitimately (¢.e. when 
opposite forms are united) than when crossed illegiti- 
mately. 


Supplementary Note on some wild hybrid Verbascums. 


In an early part of this chapter I remarked that few 
other instances could be given of a hybrid spontane- 
ously arising in such large numbers, and over so wide an 
extent of country, as that of the common oxlip ; but per- 
haps the number of well-ascertained cases of naturally 


76 UYBRID VERBASCUMS. Crap. IL. 


produced hybrid willows is equally great.* Numerous 
spontaneous hybrids between several species of Cistus, 
found near Narbonne, have been carefully described 
by M. Timbal-Lagrave,t and many hybrids between an 
Aceras and Orchis have been observed by Dr. Weddell. 
In the genus Verbascum, hybrids are supposed to have 
often originated§ in a state of nature ; some of these un- 
doubtedly are hybrids, and several hybrids have origi- 
nated in gardens; but most of these cases require,|| as 
Gartner remarks, verification. Hence the following 
case is worth recording, more especially as the two 
species in question, V. thapsus and lychnitis, are per- 
fectly fertile when insects are excluded, showing that 
the stigma of each flower receives its own pollen. 
Moreover the flowers offer only pollen to insects, and 
have not been rendered attractive to them by secret- 
ing nectar. 

I transplanted a young wild plant into my garden 
for experimental purposes, and when it flowered it 
plainly differed from the two species just mentioned 
and from a third which grows in this neighbourhood. I 
thought that it was a strange variety of V. thapsus. It 
attained the height (by measurement) of 8 feet! It 
was covered with a net, and ten flowers were fertilised 
with pollen from the same -plant; later in the season, ~ 
when uncovered, the flowers were freely visited by 
pollen-collecting bees; nevertheless, although many 
capsules were produced, not one contained a single 
seed. During the following year this same plant was 


* Max Wichura, ‘ Die Bastard- § See, for instance, the *‘ Eng- 
befruchtung, &c., der Weiden, lish Flora,’ by Sir J. E. Smith, 
1865. 1824, vol. i. p. 307. 

+ ‘Mém. del Acad. des Sciences || See Gartner, ‘ Bastarderzeu- 


de Toulouse,’ 5° série, tom. v. p.28. gung,’ 1849, p. 590. 
t ‘Annales des Sc. Nat.’ 3° 
série, Bot. tom. xviii. p. 6. 


Cuar. I. HYBRID VERBASCUMS. ie i: 


left uncovered near plants of V. thapsus and lychnitis ; 
but again it did not produce a single seed. Four 
flowers, however, which were repeatedly fertilised 
with pollen of V. lychnitis, whilst the plant was tem- 
porarily kept under a net, produced four capsules, 
which contained five, one, two, and two seeds; at the 
same time three flowers were fertilised with pollen of 
V. thapsus, and these produced two, two, and three 
seeds. To show how unproductive these seven capsules 
were, I may state that a fine capsule from a plant of 
V. thapsus growing close by contained above 700 seeds. 
These facts led me to search the moderately-sized field 
whence my plant had been removed, and I found in it 
many plants of V. thapsus and lychnitis as well as 
thirty-three plants intermediate in character between 
these two species. These thirty-three plants differed 
much from one another. In the branching of the stem 
they more closely resembled V. lychnitis than V. thapsus, 
but in height the latter species. In the shape of their 
leaves they often closely approached V. lychnitis, but 
“some had leayes extremely woolly on the upper surface 
and decurrent like those of V. thapsus; yet the degree 
of woolliness and of decurrency did not always go 
together. In the petals being flat and remaining 
open, and in the manner in which the anthers of the 
longer stamens were attached to the filaments, these 
plants all took more after V. lychnitis than V. thapsus. 
In the yellow colour of the corolla they all resembled 
the latter species. On the whole, these plants appeared 
to take rather more after V. lychnitis than V. thapsus. 
On the supposition that they were hybrids, it is not an 
anomalous circumstance that they should all have pro- 
duced yellow flowers; for Gartner crossed white and 
yellow-flowered varieties of Verbascum, and the off- 
spring thus produced never bore flowers of an inter- 


78 HYBRID VERBASCUMS. Cuar. II. 


mediate tint, but either pure white or pure yellow 
flowers, generally of the latter colour.* 

My observations were made in the autumn; so that 
I was able to collect some half-matured capsules from 
twenty of the thirty-three intermediate plants, and 
likewise capsules of the pure V. lychnitis and thapsus 
growing in the same field. All the latter were filled 
with perfect but immature seeds, whilst the capsules of 
the twenty intermediate plants did not contain one 
single perfect seed. These plants, consequently, were 
absolutely barren. From this fact,—from the one plant 
which was transplanted into my garden yielding when 
artificially fertilised with pollen from V. lychnitis and 
thapsus some seeds, though extremely few in number,— 
from the circumstance of the two pure species growing 
in the same field,—and from the intermediate character 
of the sterile plants, there can be no doubt that they 
were hybrids. Judging from the position in which 
they were chiefly found, I am inclined to believe they 
were descended from V. thapsus as the seed-bearer, and 
V.lychnitis as the pollen-bearer. 

It is known that many species of Verbascum, when 
the stem is jarred or struck by a stick, cast off their 
- flowers.| This occurs with V. thapsus, as I have re- 
peatedly observed. The corolla first separates from its 
attachment, and then the sepals spontaneously bend 
inwards so as to clasp the ovarium, pushing off the 
corolla by their movement, in the course of two or 
three minutes. Nothing of this kind takes place with 
young barely expanded flowers. With Verbascum lych- 
nitis and, as I believe, V. phaeniceum the corolla is not cast 


* ‘ Bastarderzeugung, p. 307. Smith, vol. ii. p. 210. I was 

+ This was first observed by cuided to these references by the 
Correa de Serra: see Sir J. E. Rev. W. A. Leighton, who ob- 
Smith's ‘ English Flora, 1824, vol. _ served this same phenomenon with 
i. p. 311; also ‘Life of SirJ. E.  V. virgatum. 


Cuar. IL. HYBRID VERBASCUMS. 79 


off, however often and severely the stem may be struck. 
In this curious property the above-described hybrids 
took after V. thapsus; for I observed, to my surprise, that 
when I pulled off the flower-buds round the flowers 
which I wished to mark with a thread, the slight jar 
invariably caused the corollas to fall off. 

These hybrids are interesting under several points of 
view. First, from the number found in various parts 
of the same moderately-sized field. That they owed their 
origin to insects flying from flower to flower, whilst col- 
lecting pollen, there can be no doubt. Although in- 
sects thus rob the flowers of a most precious substance, 
yet they do great good; for, as I have elsewhere 
shown,* the seedlings of V. thapsus raised from flowers 
fertilised with pollen from another plant, are more 
vigorous than those raised from self-fertilised flowers. 
But in this particular instance the insects did great 
harm, as they led to the production of utterly barren 
plants. Secondly, these hybrids are remarkable from 
differing much from one another in many of their 
characters; for hybrids of the first generation, if 
raised from uncultivated plants, are generally uni- 
form in character. That these hybrids belonged to 
the first generation we may safely conclude, from the 
absolute sterility of all those observed by me in a state 
of nature and of the one plant in my garden, excepting 
when artificially and repeatedly fertilised with pure 
pollen, and then the number of seeds produced was 
extremely small. As these hybrids varied so much, an 
almost perfectly graduated series of forms, connecting 
together the two widely distinct parent-species, could 
easily have been selected. This case, like that of 
the common oxlip, shows that botanists ought to be 


* «The Effects of Cross and Self-fertilisation,’ 1876, p. 89. 


80 HYBRID VERBASCUMS. Cuapr. IT. 


cautious in inferring the specific identity of two forms 
from the presence of intermediate gradations; nor 
would it be easy in the many cases in which hybrids are 
moderately fertile to detect a slight degree of sterility in 
such plants growing in a state of nature and liable to be 
fertilised by either parent-species. Thirdly and lastly, 
these hybrids offer an excellent illustration of a state- 
ment made by that admirable observer Gartner, namely, 
that although plants which can be crossed with ease 
generally produce fairly fertile offspring, yet well- 
pronounced exceptions to this rule occur; and here we 
have two species of Verbascuin which evidently cross 
with the greatest ease, but produce hybrids which are 
excessively sterile. 


Cuar. III. *LINUM GRANDIFLORUM. 81 


CHAPTER III. 
HererostyLeD Diworruic PLANts—continued. 


Linum grandiflorum, long-styled form utterly sterile with own-form 
pollen—Linum perenne, torsion of the pistils in the long-styled 
form alone—Homostyled species of Linum—Pulmonaria officinalis, 
singular difference in self-fertility between the English and German 
long-styled plants—Pulmonaria angustifolia shown to be a distinct 
species, long-styled form completely self-sterile—Polygonum fago- 
pyrum—Various other heterostyled genera—Rubiacee—Mitchella 
repens, fertility of the flowers in pairs—Houstonia—Faramea, 
remarkable difference in the pollen-grains of the two forms ; tor- 
sion of the stamens in the short-styled form alone; development 
not as yet perfect—The heterustyled structure in the several 
Rubiaceous genera not due to desceut in common. 


Ir has long been known* that several species of 
Linum present two forms, and having observed this 
fact in L. flavum more than thirty years ago, I was 
led, after ascertaining the nature of heterostylism in 
Primula, to examine the first species of Linum which 
I met with, namely, the beautiful L. grandiflorum. 
This plant exists under two forms, occurring in about 
equal numbers, which differ little in structure, but 
greatly in function. The foliage, corolla, stamens, and 
pollen-grains (the latter examined both distended with 
water and dry) are alike in the two forms (Fig. 4). 
The difference is confined to the pistil; in the short- 
styled form the styles and the stigmas are only about 
half the length of those in the long-styled. A more 


* Treviranus has shown that original paper, ‘Bot. Zeitung,’ 
this is the case in hisreview of my 1863, p. 189. 


* . 


82 HETEROSTYLED DIMORPHIC PLANTS. Cuap. II. 


important distinction is, that the five stigmas in the 
short-styled form diverge greatly from one another, 
and pass out between the filaments of the stamens, 


Fig. 4. 


Long-styled form. Short-styled form. 
8s stigmas, 
LINUM GRANDIFLORUM. 


and thus lie within the tube of the corolla. In the 
long-styled form the elongated stigmas stand nearly 
upright, and alternate with the anthers. In this latter 
form the length of the stigmas varies considerably, 
their upper extremities projecting even a little above 
the anthers, or reaching up*only to about their middle. 
Nevertheless, there is never the slightest difficulty in ~ 
distinguishing between the two forms ; for, besides the 
difference in the divergence of the stigmas, those of 
the short-styled form never reach even to the bases 
of the anthers, In this form the papille on the stig- 
matic surfaces are shorter, darker-coloured, and more 
crowded together than in the long-styled form; but 
’ these differences seem due merely to the shortening 
of the stigma, for in the varieties of the long-styled 
form with shorter stigmas, the papillee are more crowded 
and darker-coloured than in those with the longer 


Cuapr. III. LINUM GRANDIFLORUM. 83 


stigmas. Considering the slight and variable differ- 
ences between the two forms of this Linum, it is not 
surprising that hitherto they have been overlooked. 

In 1861 I had eleven plants in my garden, eight of 
which were long-styled, and three short-styled. Two 
very fine long-styled plants grew in a bed a hundred 
yards off all the others, and separated from them by a 
sereen of evergreens. I marked twelve flowers, and 
placed on their stigmas a little pollen from the short- 
styled plants. The pollen of the two forms is, as 
stated, identical in appearance; the stigmas of the 
long-styled flowers were already thickly covered with 
their own pollen—so thickly that I could not find one 
bare stigma, and it was late in the season, namely, 
September 15th. Altogether, it seemed almost childish 
to expect any result. Nevertheless from my experi- 
ments on Primula, I had faith, and did not hesitate to 
make the trial, but certainly did not anticipate the 
full result which was obtained. The germens of these 
twelve flowers all swelled, and wltimately six fine cap- 
sules (the seed of which germinated on the following 
year) and two poor capsules were produced; only four 
capsules shanking off. These same two long-styled 
plants produced, in the course of the summer, a 
vast number of flowers, the stigmas of which were 
covered with their own pollen; but they all proved 
absolutely barren, and their germens did not even 
swell. 

The nine other plants, six long-styled and three 
short-styled, grew not very far apart in my flower- 
garden. Four of these long-styled plants produced no 
seed-capsules; the fifth produced two; and the remain- 
ing one grew so close to a short-styled plant that 
their branches touched, and this produced twelve cap- 
sules, but they were poor ones. The case was different 


. 


84 HETEROSTYLED DIMOKPHIC PLANTS. Cuapr. IIL. 


with the short-styled plants. The one which grew 
close to the long-styled plant produced .ninety-four 
imperfectly fertilised capsules containing a multitude 
of bad seeds, with a moderate number of good ones. 
The two other short-styled plants growing together 
were small, being partly smothered by other plants; 
they did not stand very close to any long-styled plants, 
yet they yielded together nineteen capsules. These 


facts seem to show that the short-styled plants are more’ 


fertile with their own pollen than are the long-styled, 
and we shall immediately see that this probably is the 
case. But I suspect that the difference in fertility be- 
tween the two forms was in this instance in part due to 
a distinct cause. I repeatedly watched the flowers, and 
only once saw a humble-bee momentarily alight on 
one, and then fly away. If bees had visited the several 
plants, there cannot be a doubt that the four long- 
styled plants, which did not produce a single capsule, 
would have borne an abundance. But several times I 
saw small diptera sucking the flowers; and these 
insects, though not visiting the flowers with anything 
like the regularity of bees, would carry a little pollen 
from one form to the other, especially when growing 
near together; and the stigmas of the short-styled 
plants, diverging within the tube of the corolla, would 
be more likely than the upright stigmas of the long- 
styled plants, to receive a small quantity of pollen if 
brought to them by small insects. Moreover from the 
greater number of the long-styled than of the short- 
styled plants in the garden, the latter would be more 
likely to receive pollen from the long-styled, than the 
long-styled from the short-styled. 

In 1862 [ raised thirty-four plants of this Linum in a 
hot-bed ; and these consisted of seventeen long-styled 
and seventeen short-styled forms. Seed sown later in the 


i od 


Cuap. III. LINUM GRANDIFLORUM. 85 


flower-garden yielded seventeen long-styled and twelve 
short-styled forms. These facts justify the statement 
that the two forms are produced in about equal num- 
bers. The thirty-four plants of the first lot were kept 
under a net which excluded all insects, except such 
minute ones as Thrips. I fertilised fourteen long-styled 
flowers legitimately with pollen from the short-styled, 
and got eleven fine seed-capsules, which contained on 
an average 8°6 seeds per capsule, but only 5:6 appeared 
to be good. It may be well to state that ten seeds is 
the maximum production for a capsule, and that our 
climate cannot be very favourable to this North-African 
plant. On three occasions the stigmas of nearly a 
hundred flowers were fertilised illegitimately with their 
own-form pollen, taken from separate plants, so as to 
prevent any possible ill effects from close inter-breed- 
ing. Many other flowers were also produced, which, as 
before stated, must have received plenty of their own 
pollen; yet from all these flowers, borne by the seven- 
teen long-styled plants, only three capsules were pro- 
duced. One of these included no seed, and the other 
two together gave only five good seeds. It is probable 
that this miserable product of two half:fertile capsules 


_ from the seventeen plants, each of which must have 


produced at least fifty or sixty flowers, resulted from 
their fertilisation with pollen from the short-styled 
plants by the aid of Thrips; for I made a great 
mistake in keeping the two forms under the same net, 
with their branches often interlocking ; and it is sur- 
prising that a greater number of flowers were not 
accidentally fertilised. 

. Twelve short-styled flowers were in this instance 
castrated, and afterwards fertilised legitimately with 
pollen from the long-styled form; and they produced 
seven fine capsules. ‘These included on an average 


86 HETEROSTYLED DIMORPHIC PLANTS. Cuar. III. 


7°6 seeds, but of apparently good seed only 4:3 per 
capsule. At three separate times nearly a hundred 
flowers were fertilised illegitimately with their own- 
form pollen, taken from separate plants; and nu- 
merous other flowers were produced, many of which 
must have received their own pollen. Irom all these 
flowers on the seventeen short-styled plants only fifteen 
capsules were produced, of which only eleven con- 
tained any good seed, on an average 4°2 per capsule. 
As remarked in the case of the long-styled plants, 
some even of these capsules were perhaps the product 
of a little pollen accidentally fallen from the adjoining 
flowers of the other form on to the stigmas, or trans- 
ported by Thrips. Nevertheless the short-styled plants 
seem to be slightly more fertile with their own pollen 
than the long-styled, in the proportion of fifteen cap- 
sules to three; nor can this difference be accounted 
for by the short-styled stigmas being more liable to 
receive their own pollen than the long-styled, for the 
reverse is the case. The greater self-fertility of the 
short-styled flowers was likewise shown in 1861 by 
the plants in my flower-garden, which were lett to 
themselves, and were but sparingly visited by insects. 
On account of the probability of some of the flowers 
on the plants of both forms, which were covered under 
the same net, having been legitimately fertilised in 
an accidental manner, the relative fertility of the two 
legitimate and two illegitimate unions cannot be 
compared with certainty; but judging from the 
number of good seeds per capsule, the difference was 
at least in the ratio of 100 to 7, and probably much 
ereater. 
Hildebrand tested my results, but only on a single 


short-styled plant, by fertilismg many flowers with — ) 


their own-form pollen ; and these did not produce any 


Crap. III. LINUM GRANDIFLORUM. 87 


seed. This confirms my suspicion that some of the 
few capsules produced by the foregoing seventeen 
short-styled plants were the product of accidental 
legitimate fertilisation. Other flowers on the same 
plant were fertilised by Hildebrand with pollen from 
the long-styled form, and all produced fruit.* 

The absolute sterility (judging from the experi- 
ments of 1861) of the long-styled plants with their 
own-form pollen led me to examine into its apparent 
cause ; and the results are so curious that they are 
worth giving in detail. The experiments were tried 
on plants grown in pots and brought successively 
into the house. 

First. Pollen from a short-styled plant was placed 
on the five stigmas of a long-styled flower, and these, 
after thirty hours, were found deeply penetrated by a 
multitude of pollen-tubes, far too numerous to be 
counted; the stigmas had also become discoloured 
and twisted. I repeated this experiment on another 
flower, and in eighteen hours the stigmas were pene- 
trated by a multitude of long pollen-tubes. This is 
what might have been expected, as the union is 4 
legitimate one. The converse experiment was likewise 
tried, and pollen from a long-styled flower was placed 
on the stigmas of a short-styled flower, and in twenty- 
four hours the stigmas were discoloured, twisted, and 
penetrated by numerous pollen-tubes; and this, again, 
is what might have been expected, as the union was 
a legitimate one. 

Secondly. Pollen from a long-styled flower was placed 
on all five stigmas of a long-styled flower on a separate 
plant : after nineteen hours the stigmas were dissected, 
and only a single pollen-grain had emitted a tube, 


* «Bot. Zeitung,’ Jan. 1, 1864, p. 2. 
5 


88 HETEROSTYLED DIMORPHIC PLANTS. Cuap. ITI. 


ant this was a very short one. To make sure that the 
pollen was good, I took in this case, and in most of 
the other cases, pollen either from the same anther or 
from the same flower, and proved it to be good by 
placing it on the stigma of a short-styled plant, and 
found numerous pollen-tubes emitted. 

Thirdly. Repeated last experiment, and placed own- 
form pollen on all five stigmas of a long-styled flower ; 
after nineteen hours and a half, not one single grain 
had emitted its tube. 

Fourthly. Repeated the experiment, with the same 
result after twenty-four hours. 

Fifthly. Repeated last experiment, and, after leaving 
pollen on for nineteen hours, put on an additional 
quantity of own-form pollen on all five stigmas. After 
an interval of three days, the stigmas were examined, 
and, instead of being discoloured and twisted, they 
were straight and fresh-coloured. Only one grain had 
emitted a quite short tube, which was drawn out of 
the stigmatic tissue without being ruptured. 

The following experiments are more striking :— 

Siathly. 1 placed own-form pollen on three of the 
stigmas of a long-styled flower, and pollen from a 
short-styled flower on the other two stigmas. After 
twenty-two hours these two stigmas were discoloured, 
slightly twisted, and penetrated by the tubes of nu- 
merous pollen-grains: the other three stigmas, covered 
with their own-form pollen, were fresh, and all the 
pollen-grains were loose; but I did not dissect the 
whole stigma. 

Seventhly. Experiment repeated in the same manner, 
with the same result. 

Eighthly. Experiment repeated, but the stigmas were 
carefully examined after an interval of only five hours 
and a half. The two stigmas with pollen from a 


Cuap. III. LINUM GRANDIFLORUM. 89 


short-styled flower were penetrated by innumerable 
tubes, which were as yet short, and the stigmas them- 
selves were not at all discoloured. The three stigmas 
covered with their own-form pollen were not pene- 
trated by a single pollen-tube. 

Ninthly. Put pollen of a short-styled flower on a 
single long-styled stigma, and own-form pollen on the 
other four stigmas; after twenty-four hours the one 
stigma was somewhat discoloured and twisted, and 
penetrated by many long tubes: the other four stigmas 
were quite straight and fresh ; but on dissecting them 
I found that three pollen-grains had protruded ney 
short tubes into the tissue. 

Tenthly. Repeated the experiment, with the same 
result after twenty-four hours, excepting that only two 
own-form grains had penetrated the stigmatic tissue 
with their tubes to a very short depth. The one 
stigma, which was deeply penetrated by a multitude 
of tubes from the short-styled pollen, presented a 
conspicuous difference in being much curled, half- 
shrivelled, and discoloured, in comparison with the 
other four straight and bright pink stigmas. 

I could add other experiments; but those now 
given amply suffice to show that the pollen-grains of _ 
a short-styled flower placed on the stigma of a long- 
styled flower emit a multitude of tubes after an in- 
terval of from five to six hours, and penetrate the 
tissue ultimately to a great depth; and that after 
twenty-four hours the stigmas thus penetrated change 
colour, become twisted, and appear half-withered. On 
the other hand, pollen-grains from a long-styled flower 
placed on its own stigmas, do not emit their tubes 
after an interval of a day, or even three days; or at 
most only three or four grains out of a multitude emit 
their tubes, and these apparently never penetrate the 


90 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III. 


stigmatic tissue deeply, and the stigmas themselves 
do not soon become discoloured and twisted. 

This seems to me a remarkable physiological fact. 
The pollen-grains of the two forms are undistinguish- 
able under the microscope; the stigmas differ only in 
length, degree of divergence, and in the size, shade of 
colour, and approximation of their papillee, these latter 
differences being variable and apparently due merely 
to the degree of elongation of the stigma. Yet we 
plainly see that the two kinds of pollen and the two 
stigmas are widely dissimilar in their mutual reaction 
—the stigmas of each form being almost powerless on 
their own pollen, but causing, through some myste- 
rious influence, apparently by simple contact (for I 
could detect no viscid secretion), the pollen-grains of 
the opposite form to protrude their tubes. It may be 
said that the two pollens and the two stigmas mutually 
recognise each other by some means. Taking fertility 
as the criterion of distinctness, it is no exaggeration to 
say that the pollen of the long-styled Linum grandi- 
jlorum (and conversely that of the other form) has been 
brought to a degree of differentiation, with respect to 
its action on the stigma of the same form, correspond- 
ing with that existing between the pollen and stigma 
of species belonging to distinct genera. 

Linum perenne.—This species is conspicuously hetero- 
styled, as has been noticed by several authors. The 
pistil in the long-styled form is nearly twice as long as 
that of the short-styled. In the latter the stigmas are 
smaller and, diverging to a greater degree, pass out 
low down between the filaments. I could detect no 
difference in the two forms in the size of the stigmatic 
papillae. In the long-styled form alone the stigmatic 
surfaces of the mature pistils twist round, so as to face 
the circumference of the flower; but to this point I 


Cuapr. IIT. LINUM PERENNE. 91 


shall presently return. Differently from what occurs in 
L. grandiflorum, the long-styled flowers have stamens 
hardly more than half the length of those in the short- 
styled. The size of the pollen-grains is rather variable ; 
after some doubt, I have come to the conclusion that 
there is no uniform difference between the grains in 
the two forms. The long stamens in the short-styled 
form project to some height above the corolla, and 
their filaments are coloured blue apparently from ex- 
posure tothe light. The anthers of the longer stamens 
correspond in height with the lower part of the stigmas 
of the long-styled flowers; and the anthers of the 
shorter stamens of the latter correspond in the same 
manner in height with the stigmas of the short-styled 
flowers. 

I raised from seed twenty-six plants, of which twelve 
proved to be long-styled and fourteen short-styled. 
They flowered well, but were not large plants. <As I 
did not expect them to flower so soon, I did not trans- 
plant them, and they unfortunately grew with their 
branches closely interlocked. All the plants were 
covered under the same net, excepting one of each 
form. Of the flowers on the long-styled plants, twelve 
were illegitimately fertilised with their own-form pol- 
len, taken in every case from a separate plant ; and not 
one set a seed-capsule: twelve other flowers were legi- 
timately fertilised with pollen from short-styled flowers ; 
and they set nine capsules, each including on an 
average 7 good seeds, ten being the maximum number 
eyer produced. Of the flowers on the short-styled 
plants, twelve were illegitimately fertilised with own- 
form pollen, and they yielded one capsule, including 
only 3 good seeds; twelve other flowers were legiti- 
mately fertilised with pollen from long-styled flowers, 
and these produced nine capsules, but one was bad ; 


92 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IIL. 


the eight good capsules contained on an ayerage 8 
good seeds each. Judging from the number of seeds 
per capsule, the fertility of the two legitimate to that 
of the two illegitimate unions is as 100 to 20. 

The numerous flowers on the eleven long-styled 
plants under the net, which were not fertilised, produced 
only three capsules, including 8, 4, and 1 good seeds. 
Whether these three capsules were the product of acci- 
dental legitimate fertilisation, owing to the branches 
of the-plants of the two forms interlocking, I will not 
pretend to decide. The single long-styled plant which 
was left uncovered, and grew close by the uncovered 
short-styled plant, produced five good pods; but it 
was a poor and small plant. 

The flowers borne on the thirteen short-styled plants 
under the net, which were not fertilised, produced 
twelve capsules, containing on an average 5°6 seeds. 
As some of these capsules were very fine, and as five 
were borne on one twig, I suspect that some minute 
insect had accidentally got under the net and had 
brought pollen from the other form to the flowers 
which produced this little group of capsules. The one 
uncovered short-styled plant which grew close to the 
uncovered long-styled plant yielded twelve capsules. 

From these facts we have some reason to believe, as 
in the case of L. grandiflorum, that the short-styled 
plants are in a slight degree more fertile with their 
own pollen than are the long-styled plants. Anyhow 
we have the clearest evidence, that the stigmas of each 
form require for full fertility that pollen from the sta- 
mens of corresponding height belonging to the opposite 
form should be brought to them. 

Hildebrand, in the paper lately referred to, confirms 
my results. He placed a short-styled plant in his 
house, and fertilised about 20 flowers with their own 


e 


Crap. ILL. LINUM PERENNE. 93 


pollen, and about 30 with pollen from another plant 
belonging to the same form, and these 50 flowers did 
not set a single capsule. On the other hand he ferti- 
lised about 30 flowers with pollen from the long-styled 
form, and these, with the exception of two, yielded 
capsules, containing good seeds. 

It is a singular fact, in contrast with what occurred 
in the case ot L. grandiflorum, that the pollen-grains of 
both forms of LD. perenne, when placed on their own- 
form stigmas, emitted their tubes, though this action 
did not lead to the production of seeds. After an 
interval of eighteen hours, the tubes penetrated the 
stigmatic tissue, but to what depth I did not ascertain. 
In this case the impotence of the pollen-grains on their 
own stigmas must have been due either to the tubes 
not reaching the ovules, or to their not acting pro- 
perly after reaching them. 

The plants both of L. perenne and grandiflorum grew, 
as already stated, with their branches interlocked, and 
with scores of flowers of the two forms close together ; 
they were covered by a rather coarse net, through which 
the wind, when high, passed ; and such minute insects 
as Thrips could not, of course, be excluded ; yet we have 
seen that the utmost possible amount of accidental fer- 
tilisation on seventeen long-styled plants in the one 
ease, and on eleven long-styled plants in the other, 
resulted in the production, in each case, of three 
poor capsules; so that when the proper insects are 
excluded, the wind does hardly anything in the way of 
carrying pollen from plant to plant. I allude to this 
fact because botanists, in speaking of the fertilisation 
of various flowers, often refer to the wind or to insects 
as if the alternative were indifferent. This view, ac- . 
cording to my experience, is entirely erroneous. When 
the wind is the agent in carrying pollen, either from 


94 HETEROSTYLED DIMORPHIC PLANTS. Cuape. III, 


one sex to the other, or from hermaphrodite to herma- 
phrodite, we can recognise structure as manifestly ad- 
apted to its action as to that of insects when these are 
the carriers. We see adaptation to the wind in the in- 
coherence of the pollen,—in the inordinate quantity 
produced (as in the Coniferee, Spinage, &c.),—in the 
dangling anthers well fitted to shake out the pollen,— 
in the absence or small size of the perianth,—in the 
protrusion of the stigmas at the period of fertilisation, 
—in the flowers being produced before they are hidden 
by the leaves,—and in the stigmas being downy or 
plumose (as in the Graminew, Docks, &c.), so as to 
secure the chance-blown grains. In plants which are 
fertilised by the wind, the flowers do not secrete nectar, 
their pollen is too incoherent to be easily collected by 
insects, they have not bright-coloured corollas to serve 
as guides, and they are not, as far as I have seen, 
visited by insects. When insects are the agents of fer- 
tilisation (and this is incomparably the more frequent 
ease with hermaphrodite plants), the wind plays no 
part, but we see an endless number of adaptations to 
ensure the safe transport of the pollen by the living 
workers. These adaptations are most easily recognised 
in irregular flowers; but they are present in regular 
flowers, of which those of Linum offer a good instance, 
as I will now endeavour to show. 

I have already alluded to the rotation of each sepa- 
rate stigma in the long-styled form of Linwm perenne. 
In both forms of the other heterostyled species and in 
the homostyled species of Linum which I have seen, 
the stigmatic surfaces face the centre of the flower, 
with the furrowed backs of the stigmas, to which the 
styles are attached, facing outwards. This is the ease 
with the stigmas of the long-styled flowers of J. 
perenne whilst in bud. But by the time the flowers 


Cuar. IIL. LINUM PERENNE. 95 


have expanded, the five stigmas twist round so as to 
face the circumference, owing to the torsion of that 
part of the style which lies beneath the stigma.. I 
should state that the five stigmas do not always turn 
round completely, two or three sometimes facing 
only obliquely outwards. My observations were made 
during October; and it is not improbable that earlier 
in the season the torsion would have been more com- 
plete ; for after two or three cold and wet days the 
movement was very imperfectly performed. The 
flowers should be examined shortly after their ex- 
pansion, as their duration is brief; as soon as they 
begin to wither, the styles become spirally twisted 
all together, the original position of the parts being 
thus lost. 

He who will compare the structure of the whole 
flower in both forms of L. perenne and grandiflorum, 
and, as I may add, of L. flavum, will not doubt about 
the meaning of this torsion of the styles in the one 
form alone of L. perenne, as well as the meaning of 
the divergence of the stigmas in the short-styled 
form of all three species. It is absolutely necessary 
as we know, that insects should carry pollen from 
the flowers of the one form reciprocally to those of 
the other. Insects are attracted by five drops of 
nectar, secreted exteriorly at the base of the stamens, 
so that to reach these drops they must insert their 
proboscides outside the ring of broad filaments, be- 
tween them and the petals. In the short-styled form 
of the above three species, the stigmas face the axis of 
the flower; and had the styles retained their original 
upright and central position, not only would the stig- 
mas haye presented their backs to the insects which 
sucked the flowers, but their front and fertile surfaces 
would have been separated from the entering insects 


96 HETEROSTYLED DIMORPHIC PLANTS. Cuar. IIT. 


by the ring of broad filaments, and would never have 
received any pollen. As it is, the styles diverge 
and pass out between the filaments. After this move- 
ment the short stigmas le within the tube of the 
corolla ; and their papillous surfaces being now turned 
upwards are necessarily brushed by every entering 
insect, and thus receive the required pollen. 

In the long-styled form of L. grandiflorum, the 
almost parallel or slightly diverging anthers and 
stigmas project a little above the tube of the somewhat 
concave flower; and they stand directly over the open 
space leading to the drops of nectar. Consequently 
when insects visit the flowers of either form (for the 
stamens in this species occupy the same position in 
both forms), they will get their foreheads or proboscides 
well dusted with the coherent pollen. As soon as they 
visit the flowers of the long-styled form they will 
necessarily leave pollen on the proper surface of the 
elongated stigmas; and when they visit the short- 
styled flowers, they will leave pollen on the upturned 
stigmatic surfaces. Thus the stigmas of both forms 
will receive indifferently the pollen of both forms ; 
but we know that the pollen algne of the opposite form 
causes fertilisation. 

In the case of L. perenne, affairs are arranged more 


perfectly ; for the stamens in the two forms stand at 


different heights, so that pollen from the anthers of 
the longer stamens will adhere to one part of an 
insect’s body, and will afterwards be brushed off by 
the rough stigmas of the longer pistils ; whilst pollen 
from the anthers of the shorter stamens will adhere to 
a different part of the insect’s body, and will afterwards 
be brushed off by the stigmas of the shorter pistils; 
and this is what is required for the legitimate fertilisa- 
tion of both forms. The corolla of L. perenne is more 


| 


Ounar. III. LINUM PERENNE. 97 


expanded than that of L. grandiflorum, and the stigmas 
of the long-styled form do not diverge greatly from 
one another; nor do the stamens of either form. 
Hence insects, especially rather small ones, will not 
insert their proboscides between the stigmas of the 
long-styled form, nor between the anthers of either 
form (Fig. 5), but will strike against them, at nearly 
right angles, with the backs of their head or thorax. 
Now, in the long-styled flowers, if each stigma did 


Fig. 5. 


4 
/ 


\ 
i) 


N 


Long-styled form of L. PERENNE, var. Austriacum in its early condition 
before the stigmas have rotated. The petals and calyx have been 
removed on the near side.* 


not rotate on its axis, insects in visiting them would 
strike their heads against the backs of the stigmas; as 
it is, they strike against that surface which is covered 


* I neglected to get drawings from published engravings. His 
made from fresh flowersof thetwo well-known skill ensures accuracy 
forms. But Mr. Fitch has made in the proportional size of the 
the above sketch of a long-styled _ parts. 
flower from dried specimens and 


98 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IL 


with papillae, with their heads already charged with 
pollen from the stamens of corresponding height 
borne by the flowers of the other form, and legitimate 
fertilisation is thus ensured. 

Thus we can understand the meaning of the torsion 
of the styles in the long-styled flowers alone, as well 
as their divergence in the short-styled flowers. 

One other point is worth notice. In botanical works 
many flowers are said to be fertilised in the bud. This 
statement generally rests, as far as I can discover, on 
the anthers opening in the bud; no evidence being 


adduced that the stigma is at this period mature, or . 


that it is not subsequently acted on by pollen brought 
from other flowers. In the case of Cephalanthera 
grandiflora I have shown* that precocious and partial 
self-fertilisation, with subsequent full fertilisation, is 
the regular course of events. The belief that the 
flowers of many plants are fertilised in the bud, that 
is, are perpetually self-fertilised, is a most effectual bar 
to understanding their real structure. J am, however, 
far from wishing to assert that some flowers, during 
certain seasons, are not fertilised in the bud; for I 
have reason to believe that this is the case. A good 
observer,f resting his belief on the usual kind of 
evidence, states that in Linum Austriacwm (which is 


heterostyled, and is considered by Planchon as a variety — 


of L. perenne) the anthers open the evening before 
the expansion of the flowers, and that the stigmas are 
then almost always fertilised. Now we know positively 
that, so far from Linwm perenne being fertilised by its 
own pollen in the bud, its own pollen is as powerless 
on the stigma as so much inorganic dust. 

Linum jflavum.—The pistil of the long-styled form 


* ‘Fertilisation of Orchids, + ‘Etudes sur la Géogr. Bot., 
p. 108.—2nd edit. 1877, p. 84. H. Lecoq, 1856, tom. y. p. 325. 


Cuar. III. LINUM FLAVUM. 99 


of this species is nearly twice as long as that of 
the short-styled; the stigmas are longer and the 
papille coarser. In the short-styled form the stigmas 
diverge and pass out between the filaments, as in the 
previous species. ‘I'he stamens in the two forms differ 
in length; and, what is singular, the anthers of the 
longer stamens are not so long as those of the other 
form ; so that in the short-styled form both the stigmas 
and the anthers are shorter than in the long-styled 
form. The pollen-grains of the two forms do not differ 
in size. As this species is propagated by cuttings, 
generally all the plants in the same garden belong to 
the same form. I have inquired, but have never heard 
of its seeding in this country. Certainly my own plants 
never produced a single seed as long as I possessed 
only one of the two forms. After considerable search 
I procured both forms, but from want of time only a few 
experiments were made. Two plants of the two forms 
were planted some way apart in my garden, and were 
not covered by nets. Three flowers on the long-styled 
plant were legitimately fertilised with pollen from the 
short-styled plant, and one of them set a fine capsule. 
No other capsules were produced by this plant. Three 
flowers on the short-styled plant were legitimately 
fertilised with pollen from the long-styled, and all 
three produced capsules, containing respectively no 
less than 8, 9, and 10 seeds. ‘Three other flowers on 
this plant, which had not been artificially fertilised, 
produced capsules containing 5, 1, and 5 seeds; and 
it is quite possible that pollen may have been 
brought to them by insects from the long-styled plant 
growing in the same garden. Nevertheless, as they 
did not yield half the number of seeds compared 
with the other flowers on the same plant which had 
been artificially and legitimately fertilised, and as the 


100 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III. 


short-styled plants of the two previous species appa- 
rently evince some slight capacity for fertilisation with 
their own-form pollen, these three capsules may have 
been the product of self-fertilisation. 

Besides the three species now described, the yellow- 
flowered L. corymbiferum is certainly heterostyled, 
as is, according to Planchon,* JL. salsoloides. This 
botanist is the only one who seems to have inferred 
that heterostylism might have some important fune- 
tional bearing. Dr. Alefeld, who has made a special 
study of the genus, says} that about half of the sixty- 
five species known to him are heterostyled. This is 
the case with L. trigynum, which differs so much from 
the other species that it has been formed by him into 
a distinct genus.{ According to the same author, 
none of the species which inhabit America and the 
Cape of Good Hope are heterostyled. 

I have examined only three homostyled species, 
namely, L. usitatissimum, angustifolium, and catharti- 
cum. I raised 111 plants of a variety of the first-named 
species, and these, when protected under a net, all 
produced plenty of seed. The flowers, according to 
H. Miiller,§ are frequented by bees and moths. With 
respect to L. catharticum, the same author shows that 
the flowers are so constructed that they can freely 
fertilise themselves; but if visited by insects they 
might be cross-fertilised. He has, however, only once 
seen the flowers thus visited during the day; but it 


* Hooker’s ‘ London Journal of 
Botany,’ 1848, vol. vii. p. 174. 
+ ‘Bot. Zeitung,’ Sep. 18th, 


Journal of Botany,’ 1848, vol. 
vii. p. 525) to be provided with 
‘“‘staminibus exsertis;’ another 


1863, p. 281. 

t It is not improbable that the 
allied genus, Hugonia, is hetero- 
styled, for one species is said 
by Planchon (Hooker’s ‘ London 


with “stylis staminibus longiori- 
bus,” and another has “stamina 
5, majora, stylos longe superantia.” 

§ ‘Die Befruchtung der Blu- 
men,’ &e., p. 168. 


ph ol at: i ae 


: 


a 
yy 


Cuar. III. PULMONARIA OFFICINALIS. 101 


may be suspected that they are frequented during 
the night by small moths for the sake of the five 
minute drops of nectar secreted. Lastly, L. Lewisii 
is said by Planchon to bear on the same plant flowers 
with stamens and pistils of the same height, and 
others with the pistils either longer or shorter than 
the stamens. This case formerly appeared to me an 
extraordinary one; but I am now inclined to believe 
that it is one merely of great variability.* 


PuLMONARIA (BORAGINEZ). 


Pulmonaria officinalis—Hildebrand has published f 
a full account of this heterostyled plant. The pistil 
of the long-styled form is twice as long as that of the 
short-styled ; and the stamens differ in a corresponding, 
though converse, manner. There is no marked dif- 
ference in the shape or state of surface of the stigma 
in the two forms. The pollen-grains of the short- 
styled form are to those of the long-styled as 9 to 7, 
or as 100 to 78, in length, and as 7 to 6 in breadth. 
They do not differ in the appearance of their contents. 
The corolla of the one form differs in shape from that 
of the other in nearly the same manner as in Primula; 
but besides this difference the flowers of the short- 
styled are generally the larger of the two. Hilde- 
brand collected on the Siebengebirge, ten wild long- 
styled and ten short-styled plants. The former bore 
289 flowers, of which 186 (i.e. 64 per cent.) had set 
fruit, yielding 1°88 seed per fruit. The ten short- 
styled plants bore 373 flowers, of which 262 (i.e. 


* Planchon, in Hooker’s‘ Lon- _ of Science,’ vol. xxxvi. Sept. 1863, 
don Journal of Botany,’ 1848, vol. _p, 284. 
vii. p. 175. See on this subject + ‘ Bot. Zeitung,’ 1865, Jan. 13, 
Ase Gray, in ‘American Journal pp. 13 


102 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III. 


70 per cent.) had set fruit, yielding 1:86 seed per 
fruit. So that the short-styled plants produced many 
more flowers, and these set a rather larger proportion 
of fruit, but the fruits themselves yielded a slightly 
lower average number of seeds than did the long- 
styled plants. The results of Hildebrand’s experiments 
on the fertility of the two forms are given in the fol- 
lowing table :— 


TABLE 19. 
Pulmonaria officinalis (from Hildebrand). 


Number Average 
Nature of Union ae of Fruit ri Seeis 
2 owers of Seeds 
fertilised. produced. per Fruit. 
Long-styled flowers, by pollen of short-)| 14 | 
styled. Legitimate union . 
Long-styled flowers, 14 by own-pollen, | 
and 16 by pollen of other paugd of same | 30 0 0 
form. Iilegitimate union | | 
Sherk-abyled (ye @ pellentp of long a 16 14 | 1°57 
styled. Legitimate union . i 
Short-styled flowers, 11 by own peel | 
14 by pollen of other Sm of same 25 | 0 0 
form. Illegitimate union 


In the summer of 1864, before I had heard of Hilde- 
brand’s experiments, I noticed some long-styled plants 
of this species (named for me by Dr. Hooker) growing 
by themselves in a garden in Surrey; and to my 
surprise about half the flowers had set fruit, several 
of which contained 2, and one contained even 3 seeds. 
These seeds were sown in my garden and eleven 
seedlings thus raised, all of which proved long-styled, 
in accordance with the usual rule in such cases. Two 
years afterwards the plants were left uncovered, no 


Cuar. IIL. PULMONARIA OFFICINALIS. 103 


other plant of the same genus growing in my garden, 
and the flowers were visited by many bees. They set 
an abundance of seeds: for instance, I gathered from a 
single plant rather less than half of the seeds which it 
had produced, and they numbered 47. Therefore this 
illegitimately fertilised plant must have produced about 
100 seeds ; that is, thrice as many as one of the wild 
long-styled plants collected on the Siebengebirge by 
Hildebrand, and which, no doubt, had been legitimately 
fertilised. In the following year one of my plants 
was covered by a net, and even under these un- 
favourable conditions it produced spontaneously a 
few seeds. It should be observed that as the flowers 
stand either almost horizontally or hang considerably 
downwards, pollen from the short stamens would be 
likely to fall on the stigma. We thus see that the 
English long-styled plants when illegitimately ferti- 
lised were highly fertile, whilst the German plants 
similarly treated by Hildebrand were completely 
sterile. How to account for this wide discordance in 
our results I know not. Hildebrand cultivated his 
plants in pots and kept them for a time in the house, 
whilst mine were grown out of doors; and he thinks 
that this difference of treatment may have caused 
the difference in our results. But this does not appear 
to me nearly a sufficient cause, although his plants 
were slightly less productive than the wild ones growing 
on the Siebengebirge. My plants exhibited no ten- 
dency to become equal-styled, so as to lose their proper 
long-styled character, as not rarely happens under 
cultivation with several heterostyled species of Pri- 
mula; but it would appear that they had been greatly 
affected in function, either by long-continued cultiva- 
tion or by some other cause. We shall see in a 
future chapter that heterostyled plants illegitimately 


104 HETEROSTYLED DIMORPHIC PLANTS. Cuap. TI. 


iertilised during several successive generations some- 
times become more self-fertile; and this may have 
been the case with my stock of the present species 
of Pulmonaria; but in this case we must assume 
that the long-styled plants were at first sufficiently 
fertile to yield some seed, instead of being absolutely 
self-sterile like the German plants. 

Pulmonaria angustifolia—Seedlings of this plant, 
. raised from plants growing wild in the Isle of Wight, 
were named for me by Dr. Hooker. It is so closely 
allied to the last species, differmg chiefly in the shape 
and spotting of the leaves, that the two have been con- 
sidered by several eminent botanists—for instance, 
Bentham—as mere varieties. But, as we shall presently 
see, good evidence can be assigned for ranking them 
as distinct. Owing to the doubts on this head, I tried 
whether the two would mutually fertilise one another. 
Twelve short-styled flowers of P. angustifolia were 
legitimately fertilised with pollen from long-styled 
plants of P. officinalis (which, as we have just seen, are 
moderately self-fertile), but they did not produce a 
single fruit. Thirty-six long-styled flowers of P. 
angustifolia were also illegitimately fertilised during 
two seasons with pollen from the long-styled P. 
officinalis, but all these flowers dropped off unim- 
pregnated. Had the plants been mere varieties of 
the same species these illegitimate crosses would — 
probably have yielded some seeds, judging from my 
success in illegitimately fertilising the long-styled 
flowers of P. officinalis; and the twelve legitimate 
crosses, instead of yielding no fruit, would almost 
certainly have yielded a considerable number, namely, 
about nine, judging from the results given in the fol- 
lowing table (20). Therefore P. officinalis and angusti- 
folia appear to be good and distinct. species, in 


a aa* 


Cuapr. IIL. PULMONARIA ANGUSTIFOLIA. 105 


conformity with other important functional differences 
between them, immediately to be described. 

The long-styled and short-styled flowers of P. angus- 
tifolia differ from one another in structure in nearly 
the same manner as those of P. officinalis. But in the 
accompanying figure a slight bulging of the corolla 


Long-styled form. Short-styled form. 


PULMONARIA ANGUSTIFOLIA. 


in the long-styled form, where the anthers are seated, 
has been overlooked. My son William, who examined 
a large number of wild plants in the Isle of Wight, 
observed that the corolla, though variable in size, was 
generally larger in the long-styled flowers than in the 


_short-styled; and certainly the largest corollas of all 


were found on the long-styled plants, and the smallest 
on the short-styled. Exactly the reverse occurs, ac- 
cording to Hildebrand, with P. officinalis. Both the 
pistils and stamens of P. angustifolia vary much in 
length ; so that in the short-styled form the distance 
between the stigma and the anthers varied from 119 
to 65 divisions of the micrometer, and in the long- 
styled from-115 to 112. From an average of seven 


106 . HETEROSTYLED DIMORPHIC PLANTS. Cuap. III. 


measurements of each form the distance between these 
organs in the long-styled is to the same distance in 
the short-styled form as 100 to 69; so that the stigma 
in the one form does not stand on a level with the 
anthers in the other. The long-styled pistil is some- 
times thrice as long as that of the short-styled ; but 
from an average of ten measurements of both, its 
length to that of the short-styled was as 100 to 56. 
The stigma varies in being more or less, though 
slightly, lobed. The anthers also vary much in 
length in both forms, but in a greater degree in the 
long-styled than in the short-styled form; many in 
the former bemg from 80 to 63, and in the latter 
from 80 to 70 divisions of the micrometer in length. 
From an average of seven measurements, the short- 
styled anthers were to those from the long-styled as 
100 to 91 in length. Lastly, the pollen-grains from 
the long-styled flowers varied between 13 and 11°5 
divisions of the micrometer, and those from the short- 
styled between 15 and 13. The average diameter of 
25 grains from the latter, or short-styled form, was 
to that of 20 grains from the long-styled as 100 to 
91. We see, therefore, that the pollen-grains from 
the smaller anthers of the shorter stamens in the long- 
styled form are, as usual, of smaller size than those 
in the other form. But what is remarkable, a larger 
proportion of the grains were small, shrivelled, and 
worthless. This could be seen by merely comparing 
the contents of the anthers from several distinct plants 
of each form. But in one instance my son found, by 
counting, that out of 193 grains from a long-styled 
flower, 53 were bad, or 27 per cent.; whilst out of 
265 grains from a short-styled flower only 18 were 
bad, or 7 per cent. From the condition of the pollen 
in the long-styled form, and from the extreme varia- 


ee 


—_,-" in 


Cuap. III. PULMONARIA ANGUSTIFOLIA. 107 


bility of all the organs in both forms, we may perhaps 
suspect that the plant is undergoing a change, and 
tending to become dicecious. 

My son collected in the Isle of Wight on two occa- 
sions 202 plants, of which 125 were long-styled and 
77 short-styled ; so that the former were the more 
numerous. On the other hand, out of 18 plants raised 
by me from seed, only 4 were long-styled and 14 
short-styled. The short-styled plants seemed to my 
son to produce a greater number of flowers than the 
long-styled; and he came to this conclusion before a 
similar statement had been published by Hildebrand 
with respect to P. officinalis. My son gathered ten 
branches from ten different plants of both forms, and 
found the number of flowers of the two forms to be as 
100 to 89, 190 being short-styled and 169 long-styled. 
With P. officinalis the difference, according to Hilde- 
brand, is even greater, namely, as 100 flowers for the 
short-styled to 77 for the long-styled plants. The 
following table shows the results of my experi- 
ments :— 

TABLE 20. 


Pulmonaria angustifolia. 


Number | Number | Average 
Nature of the Union. oe A ij ae of 
fertilised. | produced, | per Fruit. 
Long-styled flowers, by pollen pollen of sho short- 211 
styled. Legitimate union . 
Long-styled flowers, by own-form pollen — 0 
Illegitimate union | 
"| 
" Short-styled flowers, by piety: of 58 2°60 
styled. Legitimate union . 
Short-styled flowers, by own-form meet | 1°86 
Illegitimate union na 


108 HETEROSTYLED DIMORPHIC PLANTS. Cnap. III. 


We see in this table that the fertility of the two 
legitimate unions to that of the two illegitimate 
together is as 100 to 35, judged by the proportion of 
flowers which produced fruit ; and as 100 to 32, judged 
by the average number of seeds per fruit. But the 
small number of fruit yielded by the 18 long-styled 
flowers in the first line was probably accidental, and 
if so, the difference in the proportion of legitimately 
and illegitimately fertilised flowers which yield fruit is 
really greater than that represented by the ratio of 
100 to 85. The 18 long-styled flowers illegitimately 
fertilised yielded no seeds,—not even a vestige of one. 
. Two long-styled plants which were placed under a net 
produced 138 flowers, besides those which were arti- 
ficially fertilised, and none of these set any fruit ; nor 
did some plants of the same form which were pro- 
tected during the next summer. ‘T'wo other long- 
styled plants were left uncovered (all the short-styled 
plants having been previously covered up), and 
humble-bees, which had their foreheads white with 
pollen, incessantly visited the flowers, so that their 
stigmas must have received an abundance of pollen, 
yet these flowers did not produce a single fruit. We 
may therefore conclude that the long-styled plants 
are absolutely barren with their own-form pollen, 
though brought from a distinct plant. In this re- 
spect they differ greatly from the long-styled English 
plants of P. officinalis which were found by me to 
be moderately self-fertile; but they agree in their 
behaviour with the German plants of P. officinalis 
experimented on by Hildebrand. 

Eighteen short-styled flowers legitimately fertilised 
yielded, as may be seen in Table 20, 15 fruits, each 
having on an average 2°6 seeds. Four of these fruits 

contained the highest possible number of seeds, namely 


Cap. III. PULMONARIA ANGUSTIFOLIA. 109 


4, and four other fruits contained each 3 seeds. The 
12 illegitimately fertilised short-styled flowers yielded 
7 fruits, including on an average 1°86 seed; and one 
of these fruits contained the maximum number of 
4 seeds. ‘This result is very surprising in contrast 
with the absolute barrenness of the long-styled flowers 
when illegitimately fertilised; and I was thus led to 
attend carefully to the degree of self-fertility of the 
short-styled plants. A plant belonging to this form and 
covered by a net bore 28 flowers besides those which 
had been artificially fertilised, and of all these only 
two produced a fruit each including a single seed. This 
high degree of self-sterility no doubt depended merely 
on the stigmas not receiving any pollen, or not a sufii- 
cient quantity. or after carefully covering all the 
long-styled plants in my garden, several short-styled 
plants were left exposed to the visits of humble-bees, 
and their stigmas will thus have received plenty of 
short-styled pollen; and now about half the flowers, 
thus illegitimately fertilised, set fruit. I judge of this 
proportion partly from estimation and partly from 
haying examined three large branches, which had borne 
31 flowers, and these produced 16 fruits. Of the fruits 
produced 233 were collected (many being left un- 
gathered), and these included on an average 1°82 
seed. No less than 16 out of the 235 fruits included 
the highest possible number of seeds, namely 4, and 
dl included 3 seeds. So we see how highly fertile 
these short-styled plants were when illegitimately fer- 
tilised with their own-form pollen by the aid of bees. 
The great difference in the fertility of the long and 
short-styled flowers, when both are illegitimately fer- 
tilised, is a unique case, as far as I have observed with 
heterostyled plants. The long-styled flowers when thus 
fertilised are utterly barren, whilst about half of the 


110 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IIL 


short-styled ones produce capsules, and these include a 
little above two-thirds of the number of seeds yielded 
by them when legitimately fertilised. The sterility of 
the illegitimately fertilised long-styled flowers is prob- 
ably increased by the deteriorated condition of their 
pollen ; nevertheless this pollen was highly efficient 
when applied.to the stigmas of the short-styled flowers. 
With several species of Primula the short-styled 
flowers are much more sterile than the long-styled, 
when both are illegitimately fertilised; and it is a 
tempting view, as formerly remarked, that this greater 
sterility of the short-styled flowers is a special adapta- 
tion to check self-fertilisation, as their stigmas are 
eminently liable to receive their own pollen. This view 
is even still more tempting in the ease of the long- 
styled form of Linwm grandiflorum. On the otliet 
hand, with Pulmonaria angustifolia, it is evident, from 
the corolla projecting obliquely upwards, that pollen 
is much more likely to fall on, or to be carried by 
insects down to the stigma of the short-styled than of 
the long-styled flowers; yet the short-styled instead 
of being more sterile, as a protection against self-ferti- 
lisation, are far more fertile than the long-styled, 
when both are illegitimately fertilised. 

Pulmonaria azurea, according to Hildebrand, is not 
heterostyled.* 


From an examination of dried flowers of Amsinckia spectabilis, 
sent me by Prof. Asa Gray, I formerly thought that this plant, 
a member of the Boragines, was heterostyled. Tle pistil 
varies to an extraordinary degree in length, being in some 
specimens twice as long as in others, and the point of insertion 
of the stamens likewise varies. But on raising many plants 
from seed, I soon became convinced that the whole case was 
one of mere variability. The first-formed flowers are apt to 


* ‘Die Geschlechter-Vertheilung bei den Pflanzen,’ 1867, p. 37. 


Crap. III. POLYGONUM FAGOPYRUM. 111 


have stamens somewhat arrested in development, with very 
little pollen in their anthers; and in such flowers the stigma 
projects above the anthers, whilst generally it stands below and 
sometimes on a level with them. I could detect no difference 
in the size of the pollen-grain or in the structure of the stigma 
in the plants which differed most in the above respects; and all 
of them, when protected from the access of insects, yielded 
plenty of seeds. Again, from statements made by Vaucher,.and 
from a hasty inspection, I thought at first that the allied 
Anchusa arvensis and Echium vulgare were heterostyled, but soon 
saw my error. From information given me, I examined dried 
flowers of another member of the Boraginez, Arnebia hispidis- 
sima, collected from several sites, and though the corolla, to- 
gether with the included organs, differed much in length, there 
was no sign of heterostylism. 


POLYGONUM FAGOPYRUM (POLYGONACE2). 


Hildebrand has shown that this plant, the common 
Buck-wheat, is heterostyled.* In the long-styled form 
(Fig. 7), the three stigmas project considerably above 
the eight short stamens, and stand on a level with the 
anthers of the eight long stamens in the short-styled 
form; and so it is conversely with the stigmas and 
stamens of this latter form. I could perceive no differ- 
ence in the structure of the stigmas in the two forms. 
The pollen-grains of the short-styled form are to those 
of the long-styled as 100 to 82 indiameter. This plant 
is therefore without doubt heterostyled. 

I experimented only in an imperfect manner on 
the relative fertility of the two forms. Short-styled 
flowers were dragged several times over two heads 
of flowers on long-styled plants, protected under a net, 
which were thus legitimately, though not fully, ferti- 
lised. They prodticed 22 seeds, or 11 per flower-head. 

Three flower-heads on long-styled plants received 


* ‘Die Geschlechter-Vertheilung,’ &c., 1867, p. 34, 
an 


112 HETEROSTYLED DIMORPHIC PLANTS. Cuap. ITI. 


pollen in the same manner from other long-styled 
plants, and were thus illegitimately fertilised. They 
produced 14 seeds, or only 4°66 per flower-head. 

Two flower-heads on short-styled plants received 
pollen in like manner from long-styled flowers, and 
were thus legitimately fertilised. They produced 8 
seeds, or 4 per flower-head. 


Fig. 7. 


Upper figure, the long-styled form ; lower figure, the short-styled. - 
Some of the anthers have dehisced, others have not. 


POLYGONUM FAGOPYRUM. (From H. Miiller.) 


Four heads on short-styled plants similarly received 
pollen from other short-styled plants, and were thus 
illegitimately fertilised. They produced 9 seeds, or 
2°25 per flower-head. 

The results from fertilising the flower-heads in the 
above imperfect manner cannot be fully trusted; but 
I may state that the four legitimately fertilised flower- 


i 


Cuapr. III. POLYGONUM FAGOPYRUM. 113 


heads yielded on an average 7°50 seeds per head ; 
whereas the seven illegitimately fertilised heads 
yielded less than half the number, or on an average 
only 3°28 seeds. The legitimately crossed seeds from 
the long-styled flowers were finer than those from the 
illegitimately fertiliséd flowers on the same plants, in 
the ratio of 100 to 82, as shown by the weights of an 
equal number. 

‘About a dozen plants, including both forms, were 
protected under nets, and early in the season they pro- 
duced spontaneously hardly any seeds, though at this 
period the artificially fertilised flowers produced an 
abundance; but it is a remarkable fact that later in 
the season, during September, both forms became 
highly self-fertile. They did not, however, produce 
so many seeds as some neighbouring uncovered plants 
which were visited by insects. Therefore the flowers 
of neither form when left to fertilise themselves late 
in the season without the aid of insects, are nearly so 
sterile as most other heterostyled plants. A large 
number of insects, namely 41 kinds as observed by H. 
Miiller,* visit the flowers for the sake of the eight 
drops of nectar. He infers from the structure of the 
flowers that insects would be apt to fertilise them both 
illegitimately as well as legitimately; but he is mis- 
taken in supposing that the long-styled flowers cannot 
spontaneously fertilise themselves. 

Differently to what occurs in the other genera 
hitherto noticed, Polygonum, though a very large 
genus, contains, as far as is at present known, only a 
single heterostyled species, namely the present one. 
H. Miller in his interesting description of several 


* ‘Dic Befruchtung,’ &., p. 175, and ‘ Nature,’ Jan. 1, 1874, p. 166. 


114 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III. 


other species shows that P. bistorta is so strongly pro- 
terandrous (the anthers generally falling off before the 
stigmas are mature) that the flowers must be cross- 
fertilised by the many insects which visit them. Other 
species bear much less conspicuous flowers which se- 
erete little or no nectar, and consequently are rarely 
visited by insects; these are adapted for self-fertilisa- 
tion, though still capable of cross-fertilisation. <Ac- 
cording to Delpino, the Polygonacez are generally 
fertilised by the wind, instead of by insects as in the 
present genus. 


LevcosmiA BurneETrIANA (THYMELI2). 


As Prof, Asa Gray has expressed his belief * that this species 
and L. acuminata, as well as some species in the allied genus 
Drymispermum, are dimorphic or heterostyled, I procured 
from Kew, through the kindness of Dr. Hooker, two dried 
flowers of the former species, an inhabitant of the Friendly 
Islands in the Pacific. The pistil of the long-styled form is to 
that of the short-styled as 100 to 86 in length; the stigma 
projects just above the throat of the corolla, and is surrounded 
by five anthers, the tips of which reach up almost to its base; 
and lower down, within the tubular corolla, five other and 
rather smaller anthers are seated. In the short-styled form, 
the stigma stands some way down the tube of the corolla, nearly 
on a level with the lower anthers of the other form: it differs 
remarkably from the stigma of the long-styled form, in being 
more papillose, and in being longer in the ratio of 100 to 60. 
The anthers of the upper stamens in the short-styled form are 
supported on free filaments, and project above the throat of the 
corolla, whilst the anthers of the lower stamens are seated in 
the throat on a level with the upper stamens of the other form. 
The diameters of a considerable number of grains from both sets 
of anthers in both forms were measured, but they did not differ 
in any trustworthy degree. The mean diameter of twenty-two 


* ¢American Journal of Sci- ‘Journal of Botany,’ vol. iii. 1865, 
ence, 1865, p.101,and Seemann’s pp. 305. 


Cuap. IIT. MENYANTHES TRIFOLIATA. 115 


grains from the short-styled flower was to that of twenty-four 


) 
" 
} 


grains from the long-styled, as 100 to 99. The anthers of 
the upper stamens in the short-styled form appeared to be 
poorly developed, and contained a considerable number of 
shrivelled grains which were omitted in striking the above 
average. Notwithstanding the fact of the pollen-grains from 
the two forms not differing in diameter in any appreciable 
degree, there can hardly be a doubt from the great difference in 
the two forms in the length of the pistil, and especially of the 
stigma, together with its more papillose condition in the short- 
styled form, that the present species is truly heterostyled. This 
case resembles that of Linum grandiflorum, in which the sole 
difference between the two forms consists in the length of the 
pistils and stigmas. From the great length of the tubular 
corolla of Leucosmia, it is clear that the flowers are cross- 
fertilised by large Lepidoptera or by honey-sucking birds, and 
the position of the stamens in two whorls one beneath the 
other, which is a character that I have not seen in any other 
heterostyled dimorphic plant, probably serves to smear the 
inserted organ thoroughly with pollen. 


MENYANTHES TRIFOLIATA (GENTIANEZ). 


This plant inhabits marshes: my son William gathered 247 
flowers from so many distinct plants, and of these 110 were 
long-styled, and 187 short-styled. The pistil of the long-styled 
form is in length to that of the short-styled in the ratio of about 
3to2. The stigma of the former, as my son observed, is deci- 
dedly larger than that of the short-styled ; but in both forms it 
varies much in size. The stamens of the short-styled are almost 
double the length of those of the long-styled; so that their 
anthers stand rather above the level of the stigma of the long- 
styled form. The anthers also vary much in size, but seem 
often to be of larger size in the short-styled flowers. My son 
made with the camera many drawings of the pollen-grains, 
and those from the short-styled flowers were in diameter in 
nearly the ratio of 100 to 84 to those from the long-styled 
flowers. I know nothing about the capacity for fertilisation in 
the two forms; but short-styled plants, living by themselves in 
the gardens at Kew, have produced an abundance of capsules, 
yet the seeds have never germinated; and this looks as if the 
short-styled form was sterile with its own pollen. 


116 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III. 


LIMNANTHEMUM INDICUM (GENTIANEX). 


This plant is mentioned by Mr. Thwaites in his Enumeration 
of the Plants of Ceylon as presenting two forms; and he was so 
kind as to send me specimens preserved in spirits. The pistil 
of the long-styled form is nearly thrice as long (i.e. as 14 to 5) 
as that of the short-styled, and is very much thinner in the 
ratio of about 8 to 5. The foliaceous stigma is more expanded, 
and twice as large as that of the short-styled form. In the 
latter the stamens are about twice as long as those of the long- 
styled, and their anthers are larger in the ratio of 100 to 70. 
The pollen-grains, after having been long kept in spirits, were 
of the same shape and size in both forms. The ovules, accord- 
ing to Mr. Thwaites, are equally numerous (viz. from 70 to 80) 
in the two forms. 


VILLARSIA [SP. ?] (GENTIANEZ). 


Fritz Miller sent me from South Brazil dried flowers of this 
aquatic plant, which is closely allied to Limnanthemum. In the 
long-styled form the stigma stands some way above the anthers, 
and the whole pistil, together with the ovary, is in length to 
that of the short-styled form as about 3 to 2. In the latter 
form the anthers stand above the stigma, and the style is very 
short and thick; but the pistil varies a good deal in length, 
the stigma being either on a level with the tips of the sepals 
or considerably beneath them. The foliaceous stigma in 
the long-styled form is larger, with the expansions running 
farther down the style, than in the other form. One of the most 
remarkable differences between the two forms is that the anthers 
of the longer stamens in the short-styled flowers are conspicu- 
ously longer than those of the shorter stamens in the long-styled 
flowers. In the former the sub-triangular pollen-grains are 
larger; the ratio between their breadth (measured from one 
angle to the middle of the opposite side) and that of the grains 
from the long-styled flowers being about 100 to 75. Fritz 
Miiller also informs me that the pollen of the short-styled 
flowers has a bluish tint, whilst that of the long-styled is yellow. 
When we treat of Lythrum salicaria we shall find a strongly 
marked contrast in the colour of the pollen in two of the forms. 

The three genera, Menyanthes, Limnanthemum, and Villarsia, 
now described, constitute a well-marked sub-tribe of the Gen- 
tianeze. All the species, as far as at present known, are hetero- 
styled, and all inhabit aquatic or sub-aquatic stations. 


CORDIA. 117 


FoRSYTHIA SUSPENSA (OLEACEZR). 


Professor Asa Gray states that the plants of this species grow- 
ing in the Botanic Gardens at Cambridge, U-.S., are short-styled, 


' put that Siebold and Zuccarini describe the long-styled form, 


and give figures of two forms; so that there can be little doubt, 
as he remarks, about the plant being dimorphic.* I therefore 
applied to Dr. Hooker, who sent me a dried flower from Japan, 
another from China, and another from the Botanic Gardens at 
Kew. The first proved to be long-styled, and the other two 
short-styled. In the long-styled form, the pistil is in length 
to that of the short-styled as 100 to 38, the lobes of the stigma 
being a little longer (as 10 to 9), but narrower and less diver- 
gent. This last character, however, may be only a temporary 
one. There seems to be no difference in the papillose condition 
of the two stigmas. In the short-styled form, the stamens are 
in length to those of the long-styled as 100 to 66, but the anthers 
are shorter in the ratio of 87 to 100; and this is unusual, for 
when there is any difference in size between the anthers of the 
two forms, those from the longer stamens of the short-styled are 
generally the longest. The pollen-grains from the short-styled 
flowers are certainly larger, but only in a slight degree, than 
those from the long-styled, namely, as 100 to 94 in diameter. 
The short-styled form, which grows in the Gardens at Kew, has 
never there produced fruit. 

Forsythia viridissima appears likewise to be heterostyled ; for 
Professor Asa Gray says that although the long-styled form 
alone grows in the gardens at Cambridge, U.S., the published 
figures of this species belong to the short-styled form. 


Corp1A 'sp.?] (CoRDIACEs). 


Fritz Miiller sent me dried specimens of this shrub, which he 
believes to be heterostyled; and I have not much doubt that 
this is the case, though the usual characteristic differences are 
not well pronounced in the two forms. Linum grandiflorum 
shows us that a plant may be heterostyled in function in the 
highest degree, and yet the two forms may have stamens of 
equal length, and pollen-grains of equal size. In the present 
species of Cordia, the stamens of both forms are of nearly equal 


* ‘The American Naturalist,’ July 1873, p. 422. 


118 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III. 


length, those of the short-styled being rather the longest; and 
the anthers of both are seated in the mouth of the corolla. Nor 
could I detect any difference in the size of the pollen-grains, 
when dry or after being soaked in water. Thestigmas of the 
long-styled form stand clear above the anthers, and the whole 
pistil is longer than that of the short-styled, in about the ratio 
of 3 to 2. 

The stigmas of the short-styled form are seated beneath the 
anthers, and they are considerably shorter than those of the 
long-styled form. This latter difference is the most important 
one of any between the two forms. 


GiILIA ([poMopsIs) PULCHELLA VEL AGGREGATA (POLEMONI- 
ACEZ). ' 


Professor Asa Gray remarks with respect to this plant: “ the 
tendency to dimorphism, of which there are traces, or perhaps 
rather incipient manifestations in various portions of the genus, 
is most marked in G. aggregata.”* He sent me some dried 
flowers, and I procured others from Kew. They differ greatly 
in size, some being nearly twice as long as others (viz. as 30 to 
17), so that it was not possible to compare, except by calculation, 
the absolute length of the organs from different plants. More- 
over, the relative position of the stigmas and anthers is variable: 
in some long-styled flowers the stigmas and anthers were ex- 
serted only just beyond the throat of the corolla; whilst in 
others they were exserted as much as ;4; of an inch. I suspect 
also that the pistil goes on growing for some time after the 
anthers have dehisced. Nevertheless it is possible to class the 
flowers under two forms. In some of the long-styled, the length 
of pistil to that of the short-styled was as 100 to 82; but this 
result was gained by reducing the size of the corollas to the 
same scale. In another pair of flowers the difference in length 
between the pistils of the two forms was certainly greater, but 
they were not actually measured. In the short-styled flowers 
whether large or small, the stigma is seated low down within 
the tube of the corolla. The papille on the long-styled stigma 
are longer than those on the short-styled, in the ratio of 100 to 
40. The filaments in some of the short-styled flowers were, to 
those of the long-styled, as 100 to 25 in length, the free, or 


* «Proc. American Acad. of Arts and Sciences,’ June 14, 1870, p. 275. 


Cuar. III. PHLOX SUBULATA. 119 


unattached portion being alone measured; but this ratio can- 
not be trusted, owing to the great variability of the stamens. 
The mean diameter of eleven pollen-grains from long-styled 
flowers, and of twelve from the short-styled, was exactly the 
same. It follows from these several statements, that the dif- 
ference in length and state of surface of the stigmas in the 
flowers is the sole reliable evidence that this species is hetero- 
styled; for it would be rash to trust to the difference in the 
length of the pistils, seeing how variable they are. I should 
have left the case altogether doubtful, had it not been for the 
observations on the following species; and these leave little 
doubt on my mind that the present plant is truly heterostyled. 
Professor Gray informs me that in another species, G. coronopi- 
folia, belonging to the same section of the genus, he can see no 
sign of dimorphism. 


GILIA (LEPTOSIPHON) MICRANTHA. 


A few flowers sent me from Kew had been somewhat injured, 
so that I cannot say anything positively with respect to the 
position and relative length of the organs in the two forms. 
But their stigmas differed almost exactly in the same manner as 
in the last species; the papillz on the long-styled stigma being 
longer than those on the short-styled, in the ratio of 100 to 42. 
My son measured nine pollen-grains from the long-styled, and 
the same number from the short-styled form; and the mean 
diameter of the former was to that of the latter as 100 to 81. 
Considering this difference, as well as that between the stigmas 
of the two forms, there can be no doubt that this species is 
heterostyled. So probably is Gilia nudicaulis, which likewise 
belongs to the Leptosiphon section of the genus, for I hear from 
Professor Asa Gray that in some individuals the style is very 
long, with the stigma more or less exserted, whilst in others it 
is deeply included within the tube; the anthers being always 
seated in the throat of the corolla. 


PHLOX SUBULATA (POLEMONIACEZ). 


Professor Asa Gray informs me that the greater number of 
the species in this genus have a long pistil, with the stigma 
more or less exserted; whilst several other species, especially the 
annuals, have a short pistil seated low down within the tube of 
the corolla. In all the species the anthers are arranged one 


120 HETEROSTYLED DIMORPHIC PLANTS. Cuap. ILL 


below the other, the uppermost just protruding from the throat 
of the corolla. In Phlox subulata alone he has “ seen both long 
and short styles; and here the short-styled plant has (irrespec- 
tive of this character) been described as a distinct species (P. 
nivalis, P. Hentzii), and is apt to have a pair of ovules in each 
cell, while the long-styled P. subulata rarely shows more than 
one.”* Some dried flowers of both forms were sent me by him, 
and I received others from Kew, but I have failed to make 
out whether the species is heterostyled. In two flowers of 
nearly equal size, the pistil of the long-styled form was twice as 
long as that of the short-styled; but in other cases the differ- 
ence was not nearly so great. The stigma of the long-styled 
pistil stands nearly in the throat of the corolla; whilst in the 
short-styled it is placed low down—sometimes very low down 
in the tube, for it varies greatly in position. The stigma is 
more papillose, and of greater length (in one instance in the 
ratio of 100 to 67), in the short-styled flowers than in the 
long-styled. My son measured twenty pollen-grains from a 
short-styled flower, and nine from a long-styled, and the 
former were in diameter to the latter as 100 to 93; and this 
difference accords with the belief that the plant is hetero- 
styled. But the grains from the short-styled varied much in 
diameter. He afterwards measured ten grains from a distinct 
long-styled flower, and ten from another plant of the same form, 
and these grains differed in diameter in the ratio of 100 to 90. 
The mean diameter of these two lots of twenty grains was to 
that of twelve grains from another short-styled flower as 100 to 
75: here, then, the grains from the short-styled form were con- 
siderably smaller than those from the long-styled, which is the 
reverse of what occurred in the former instance, and of what is 
the general rule with heterostyled plants. The whole case is 
perplexing in the highest degree, and will not be understood 
until experiments are tried on living plants. The greater length, 
and more papillose condition of the stigma in the short-styled 
than in the long-styled flowers, looks as if the plant was hetero- 
styled; for we know that with some species—for instance, Leu- 
cosmia and certain Rubiaceze—the stigma is longer and more 
papillose in the short-styled form, though the reverse of this 
holds good in Gilia, a member of the same family with Phlox. 
The similar position of: the anthers in the two forms is some- 


* «Proc, American Acad. of Arts and Sciences,’ June 14, 1870, p. 248. 


Cuar. ITI. ERYTHROXYLUM. 121 


what opposed to the present species being heterostyled ; as is 
the great difference in the length of the pistil in several short- 
styled flowers. But the extraordinary variability in diameter of 
the pollen-grains, and the fact that in one set of flowers the 
grains from the long-styled flowers were larger than those from 
the short-styled, is strongly opposed to the belief that Phlox 
subulata is heterostyled. Possibly this species was once hetero- 
styled, but is now becoming sub-dicecious; the short-styled 
plants having been rendered more feminine in nature. This 
would account for their ovaries usually containing more ovules, 
and for the variable condition of their pollen-grains. Whether 
the long-styled plants are now changing their nature, as would 
appear to be the case from the variability of their pollen-grains, 
and are becoming more masculine, I will not pretend to con- 
jecture; they might remain as hermaphrodites, for the co- 
existence of hermaphrodite and female plants of the same 
species is by no means a rare event. 


ERYTHROXYLUM [spP. ?] (ERYTHROXYLIDZ). 


Fritz Miiller sent me from South Brazil dried flowers of this 
tree, together with the accompanying drawings, which show the 
two forms, magnified about five times, with the petals removed. 


Fig. 8. 


Long-styled form. Short-styled form. 
From a sketch by Fritz Miiller, magnified five times. 


ERYTHROXYLON [sp. ?]. 


122 HETEROSTYLED DIMORPHIC PLANTS. Cuaap. Il. 


In the long-styled form the stigmas project above the anthers, 
and the styles are nearly twice as long as those of the short- 
styled form, in which the stigmas stand beneath the anthers. 
The stigmas in many, but not in all the short-styled flowers are 
larger than those in the long-styled. The anthers of the short- 
styled flowers stand on a level with the stigmas of the other 
form; but the stamens are longer by only one-fourth or one-fifth 
of their own length than those of the long-styled. Consequently 
the anthers of the latter do not stand on a level with, but rather 
above the stigmas of the other form. Differently from what 
occurs in the following closely allied genus, Sethia, the stamens 
are of nearly equal length in the flowers of the same form. The 
pollen-grains of the short-styled flowers, measured in their dry 
state, are a little larger than those from the long-styled flowers 
iv. about the ratio of 100 to 93.* 


SETHIA ACUMINATA (ERYTHROXYLIDZ). 


Mr. Thwaites pointed out several years agof that this plant 
exists under two forms, which he designated as forma stylosa et 
staminea ; and the flowers sent to me by him are clearly hetero- 
styled. In the long-styled form the pistil is nearly twice as 
long, aud the stamens half as long as the corresponding organs 
in the short-styled form. The stigmas of the long-styled seem 
rather smaller than those of the short-styled. All the stamens 
in the short-styled flowers are of nearly equal length, whereas 
in long-styled they differ in length, being alternately a little 
longer and shorter; and this difference in the stamens of the 
two forms is probably related, as we shall hereafter see in 
the case of the short-styled flowers of Lythrum salicaria, to the 
manner in which insects can best transport pollen from the 
long-styled flowers to the stigmas of the short-styled. The 
pollen-grains from the short-styled flowers, though variable in 
size, are to those of the long-styled, as far as I could make out, 
as 100 to 83 in their longer diameter. Sethia obtusifolia is 
heterostyled like S. acuminata. 


* F. Miiller remarks in his let- 
ter to me that the flowers, of which 
he carefully examined many spe- 
cimens, are curiously variable 
in the number of their parts: 
5 sepals and petals, 10 stamens 
and 3 pistils are the prevailing 


numbers ; but the sepals and petals 
often vary from 5 to 7; the sta- 
mens from 10 to 14, and the pistils 
from 3 to 4. 

+ ‘Enumeratio Plantarum Zey- 
lanie,’ 1864, p. 54. 


, 


Cuar. III. ASGIPHILA ELATA. 128 


CRATOXYLON FORMOSUM (HyYPERICINEZ). 


Mr. Thiselton Dyer remarks that this tree, an inhabitant of 
Malacca and Borneo, appears to be heterostyled.* He sent me 
dried flowers, and the difference between the two forms is con- 
spicuous. In the long-styled form the pistils are in length to 
those of the short-styled as 100 to 40, with their globular 
stigmas about twice as thick. These stand just above the numer- 
ous anthers and a little beneath the tips of the petals. In the 
short-styled form the anthers project high above the pistils, the 
stigmas of which diverge between the three bundles of stamens, 
and stand only a little above the tips of the sepals. The 
stamens in this form are to those of the long-styled as 100 to 86 
in length; and therefore they do not differ so much in length 
as do the pistils. Ten pollen-grains from each form were 
measured, and those from the short-styled were to those from 
the long-styled as 100 to 86 in diameter. ‘This plant, therefore, 
is in all respects a well-characterised heterostyled species. 


JEGIPHILA ELATA (VERBENACEZ). 


Mr. Bentham was so kind as to send me dried flowers of this 
species and of @. mollis, both inhabitants of South America. 
The two forms differ conspicuously, as the deeply bifid stigma 
of the one, and the anthers of the other project far above the 
mouth of the corolla. In the long-styled form of the present 
species, the style is twice and a half as long as that of the short- 
styled. The divergent stigmas of the two forms do not differ 
much in length, nor as far as I could perceive in their papillae. 
In the long-styled flowers the filaments adhere to the corolla 
close up to the anthers, which are enclosed some way down 
within the tube. In the short-styled flowers the filaments are 
free above the point where the anthers are seated in the other 
form, and they project from the corolla to an equal height with 
that of the stigmas in the long-styled flowers. It is often 
difficult to measure with accuracy pollen-grains, which have 
long been dried and then soaked in water; but they here 
manifestly differed greatly in size. Those from the short-styled 
flowers were to those from the long-styled in diameter in 


* ¢ Journal of Botany,’ London, 1872, p. 26. 


124 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IIL 


about the ratio of 100 to 62. The two forms of 4. mollis 
present a like difference in the length of their pistils and 
stamens. 


ZEGIPHILA OBDURATA. 


Flowers of this’ bush were sent me from St. Catharina in 
Brazil, by Fritz Miiller, and were named for me at Kew. They 
appeared at first sight grandly heterostyled, as the stigma of 
the long-styled form projects far out of the corolla, whilst the 
anthers are seated halfway down within the tube; whereas in the 
short-styled form the anthers project from the corolla and the 
stigma is enclosed in the tube at nearly the same level with the 
anthers of the other form. The pistil of the long-styled is to 
that of the short-styled as 100 to 60 in length, and the stigmas, 
taken by themselves, as 100 to 55. Nevertheless, this plant 
cannot be heterostyled. The anthers in the long-styled form 
are brown, tough, and fleshy, and less than half the length 
of those in the short-styled form, strictly as 44 to 100 ; and 
what is much more important, they were in a rudimentary 
condition in the two flowers examined by me, and did not 
contain a single grain of pollen. In the short-styled form, the 
divided stigma, which as we have seen is much shortened, 
is thicker and more fleshy than the stigma of the long- 
styled, and is covered with small irregular projections, formed 
of rather large cells. It had the appearance of having suf- 
fered from hypertrophy, and is probably incapable of fertili- 
sation. If this be so the plant is dicecious, and judging from 
the two species previously described, it probably was once 
heterostyled, and has since been rendered dicecious by the 
pistil in the one form, and the stamens in the other having 
become functionless and reduced in size. It is, however, 
possible that the flowers may be in the same state as those of 
the common thyme and of several other Labiate, in which 
females and hermaphrodites regularly co-exist. Fritz Miller, 
who thought that the present plant was heterostyled, as I 
did at first, informs me that he found bushes in several places 
growing quite isolated, and that these were completely sterile ; 
whilst two plants growing close together were covered with 
fruit. This fact agrees better with the belief that the species is 
dicecious than that it consists of hermaphrodites and females; 
for if any one of the isolated plants had been an hermaphrodite, 
it would probably have produced some fruit. 


Cuar. III. MITCHELLA REPENS. 125 


RuBIACE. 


This great natural family contains a much larger 
number of heterostyled genera than any other one, as 
yet known. 

Mitchella repens.—Prof. Asa Gray sent me several 
living plants collected when out of flower, and nearly 
half of these proved long-styled, and the other half 
short-styled. The white flowers, which are fragrant 
and which secrete plenty of nectar, always grow in 
pairs with their ovaries united, so that the two together 
produce “a berry-like double drupe.”* In my first 
series of experiments (1864) I did not suppose that 
this curious arrangement of the flowers would have any 
influence on their fertility ; and in several instances 
only one of the two flowers in a pair was fertilised ; 
and a large proportion or all of these failed to produce 
berries. In the ensuing year both flowers of each 
pair were invariably fertilised in the same manner; 
and the latter experiments alone serve to show the 
proportion of flowers which yield berries, when legiti- 
mately and illegitimately fertilised; but for calcu- 
lating the average number of seeds per berry I have 
used those produced during both seasons. 

In the long-styled flowers the stigma projects just 
above the bearded throat of the corolla, and the 
anthers are seated some way down the tube. In the 
short-styled flowers these organs occupy reversed posi- 
tions. In this latter form the iresh pollen-grains.are 
a little larger and more opaque than those of the long- 
styled form. The results of my experiments are given 
in the following table. 


* A. Gray, ‘Manual of the Bot. of the N. United States, 1856, 
p. 172. 


_ 
bo 
(or) 


HETEROSTYLED DIMORPHIC PLANTS. Cuaap. II. 


TABLE 21. 
Mitchella repens. 


Average 
Number of | Number of | Number of 
Pairs of Drupes pro- | good Seeds 
Nature of Union. Flowers fer- | duced during | per Drupe in 
tilised during! the second all the Drupes 
the second Season. during the 
Season. | two Seasons. 
Long-styled flowers, by pollen of\! 9 3 | 4:6 
short-styled. Legitimate union), ey al | 
Long-styled flowers, by own-form 8 Seat 3 | 2-9 
pollen. Illegitimate union , } | 
ee i Se eee — 
Short-styled flowers, by pollen a 8 7 yaa 
long-styled. Legitimate union sa al 
Short-styled flowers, by aaa 9 0 2°0 
pollen. Illegitimate union 
mY Cenaes abl : 
The two rele unions to a; 17 | 15 | ae 
gether | 
-)| | 
The two ee ear unions to hiss 17 3 | o-1 
gether - | 
i 


It follows from this table that 88 per cent. of the 
paired flowers of both forms, when legitimately fer- 
tilised, yielded double berries, nineteen of which con- 
tained on an average 4°4 seeds, with a maximum in 
one of 8 seeds. Of the illegitimately fertilised paired 
flowers only 18 per cent. yielded berries, six of which 
contained on an average only 2:1 seeds, with a maxi- 
mum in one of 4 seeds. Thus the two legitimate 
unions are more fertile than the two illegitimate, 
according to the proportion of flowers which yielded 
berries, in the ratio of 100 to 20; and according to 
the average number of contained seeds as 100 to 47. 

Three long-styled and three short-styled plants were 
protected under separate nets, and they produced alto- 
gether only 8 berries, containing on an average only 


Car. ILL. BORRERIA. 127 


15 seed. Some additional berries were produced 
which contained no seeds. The plants thus treated were 
therefore excessively sterile, and their slight degree of 
fertility may be attributed in part to the action of the 
many individuals of Thrips which haunted the flowers. 
Mr. J. Scott informs me that a single plant (probably 
a long-styled one), growing in the Botanic Gardens at 
Edinburgh, which no doubt was freely visited by in- 
sects, produced plenty of berries, but how many of 
them contained seeds was not observed. 


BorRERIA, NOY. SP. NEAR VALERIANOIDES (RUBIACE2). 


Fritz Miller sent me seeds of this plant, which is 
extremely abundant in St. Catharina, in South Brazil ; 
and ten plants were raised, consisting of five long- 
styled and five short-styled. The pistil of the long- 
styled flowers projects just beyond the mouth of the 
corolla, and is thrice as long as that of the short- 
styled, and the divergent stigmas are likewise rather 
larger. The anthers in the long-styled form stand 
low down within the corolla, and are quite hidden. 
In the short-styled flowers the anthers project just 
above the mouth of the corolla, and the stigma stands 
low down within the tube. Considering the great 
difference in the length of the pistils in the two forms, 
it is remarkable that the pollen-grains differ very little 
in size, and Fritz Miller was struck with the same 
fact. In a dry state the grains from the short-styled 
flowers could just be perceived to be larger than those 
from the long-styled, and when both were swollen by 
immersion in water, the former were to the latter in 
diameter in the ratio of 100 to 92. In the long-styled 
flowers beaded hairs almost fill up the mouth of the 
corolla and project above it; they therefore stand 
above the anthers and beneath the stigma. In the 


128  HETEROSTYLED DIMORPHIC PLANTS. Cuap. III. 


short-styled flowers a similar brush of hairs is situated 
low down within the tubular corolla, above the stigma 
and beneath the anthers. The presence of these beaded 
hairs in both forms, though occupying such different 
positions, shows that they are probably of considerable 
functional importance. They would serve to guard the 
stigma of each form from its own pollen; but in 
accordance with Prof. Kerner’s view* their chief use 
probably is to prevent the copious nectar being stolen 
by small crawling insects, which could not render any 
service to the species by carrying pollen from one form 
to the other. 

The flowers are so small and so crowded together 
that I was not willing to expend time in fertilising 
them separately ; but I dragged repeatedly heads of 
short-styled flowers over three long-styled flower-heads, 
which were thus legitimately fertilised ; and they pro- 
duced many dozen fruits, each containing two good 
seeds. I fertilised in the same manner three heads 
on the same long-styled plant with pollen from another 
long-styled plant, so that these were fertilised illegiti- 
mately, and they did not yield a single seed. Nor did 
this plant, which was of course protected by a net, 
bear spontaneously any seeds. Nevertheless another 
long-styled plant, which was carefully protected, pro- 
duced spontaneously a very few seeds; so that the 
long-styled form is not always quite sterile with its 
own pollen. 


FaRAMEA [sp.?] (RUBIACEZ). 


Fritz Miller has fully described the two forms of this 
remarkable plant, an inhabitant of South Brazil.f In 


* ‘Die Schutzmittel der Blii- t ‘ Bot. Zeitung,’ Sept. 10, 1869, 
then gegen unberufene Giste,’ p. 606. 
1876, p. 37. 


Cuap. ITI. FARAMEA. 129 


the long-styled form the pistil projects above the 
corolla, and is almost exactly twice as long as that of 
the short-styled, which is included within the tube. 
The former is divided into two rather short and broad 
stigmas, whilst the short-styled pistil is divided into 
two long, thin, sometimes much curled stigmas. The 
stamens of each form correspond in height or length 
with the pistils of the other form. The anthers of 
the short-styled form are a little larger than those 
of the long-styled; and their pollen-grains are to 
those of the other form as 100 to 67 in diameter. 
But the pollen-grains of the two forms differ in a 
much more remarkable manner, of which no other 


Fig. 9. 


fin 


Short-styled form. Long-styled form. 
Outlines of flowers from dried specimens. Pollen-grains, magnified 180 
times, by Fritz Miiller, 


FARAMEA [sp. ?]. 


instance is known; those from the short-styled flowers 
being covered with sharp points; the smaller ones 


130 HETEROSTYLED DIMORPHIC PLANTS. Cnar. Il 


from the long-styled being quite smooth. Fritz Miller 
remarks that this difference between the pollen-grains 
of the two forms is evidently of service to the plant ; 
for the grains from the projecting stamens of the short- 
styled form, if smooth, would have been lable to be 
blown away by the wind, and would thus have been 
lost ; but the little points on their surfaces cause them 
to cohere, and at the same time favour their adhesion 
to the hairy bodies of insects, which merely brush 
against the anthers of these stamens whilst visiting 
the flowers. On the other hand, the smooth grains 
of the long-styled flowers are safely included within 
the tube of the corolla, so that they cannot be blown 
away, but are almost sure to adhere to the proboscis of 
an entering insect, which is necessarily pressed close 
against the enclosed anthers. 

It may be remembered that in the long-styled form 
of Linum perenne each separate stigma rotates on its 
own axis, when the flower is mature, so as to turn its 
papillose surface outwards. There can be no doubt 
that this movement, which is confined to the long- 
styled form, is effected in order that the proper sur 
face of the stigma should receive pollen brought by 
insects from the other form. Now with Faramea, as 
Fritz Miller shows, it is the stamens which rotate on 
their axes in one of the two forms, namely, the short- 
styled, in order that their pollen should be brushed off 
by insects and transported to the stigmas of the other 
form. In the long-styled flowers the anthers of the 
short enclosed stamens do not rotate on their axes, 
but dehisce on their inner sides, as is the common 
rule with the Rubiacee ; and this is the best position 
for the adherence of the pollen-grains to the proboscis 
of an entering insect. Fritz Miller therefore infers 
that as the plant became heterostyled, and as the 


Ouapr. III. RUBIACE. 131 


stamens of the short-styled form increased in length, 
they gradually acquired the highly beneficial power 
of rotating on their own axes. But he has further 
shown, by the careful examination of many flowers, 
that this power has not as yet been perfected; and, 
consequently, that a certain proportion of the pollen 
is rendered useless, namely, that from the anthers 
which do not rotate properly. It thus appears that 
the development of the plant has not as yet been com- 
pleted; the stamens have indeed acquired their proper 
length, but not their full and perfect power of rotation.* 

The several points of difference in structure between 
the two forms of Faramea are highly remarkable. 
Until within a recent period, if any one had been 
shown two plants which differed in a uniform manner 
in the length of their stamens and pistils,—in the 
form of their stigmas,—in the manner of dehiscence 
and slightly in the size of their anthers,—and to an 
extraordinary degree in the diameter and structure of 
‘their pollen-grains, he would have declared it impos- 
sible that the two could have belonged to one and the 
same species. 


SUTERIA (species unnamed in the herbarium at Kew) 
(RUBIACEZ). 


I owe to the kindness of Fritz Miiller dried flowers of this 
plant from St. Catharina, in Brazil. In the long-styled form the 
stigma stands in the mouth of the corolla, above the anthers, 


* Fritz Miiller gives another 
instance of the want of absolute 
perfection in the flowers of another 
member of the Rubiacez, namely, 
Posoqueria fragrans, which is 
adapted in a most wonderful man- 
ner for cross-fertilisation by the 
agency of moths. (See ‘ Bot. 
Zeitung, 1866, No. 17.) In ac- 


cordance with the nocturnal habits 
of these insects, most of the flowers 
open only during the night; but 
some open in the day, and the 
pollen of such flowers is robbed, as 
Fritz Miiller has often seen, by 
humble-bees and other insects, 
without any benefit being thus 
conferred on the plant. 


1382 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III. 


which latter are enclosed within the tube, but only a short way 
down. In the short-styled form the anthers are placed in the 
mouth of the corolla above the stigma, which occupies the same 
position as the anthers in the other form, being seated only a 
short way down the tube. Therefore the pistil of the long-styled 
form does not exceed in length that of the short-styled in © 
nearly so great a degree as in many other Rubiacez. Never- 
theless there is a considerable difference in the size of the pollen- 
grains in the two forms; for, as Fritz Miller informs me, those 
of the short-styled are to those of the long-styled as 100 to 
75 in diameter. 


HOUSTONIA C@RULEA (RUBIACEZ). 


Prof. Asa Gray has been so kind as to send me an abstract of 
some observations made by Dr. Rothrock on this plant. The 
pistil is exserted in the one form and the stamens in the 
other, as has long been observed. The stigmas of the long- 
styled form are shorter, stouter, and far more hispid than in 
the other form. The stigmatic hairs or papille on the former 
are ‘04 mm., and on the latter only ‘023 mm. in length. In the 
short-styled form the anthers are larger, and the pollen-grains, 
when distended with water, are to those from the long-styled 
form as 100 to 72 in diameter. 

Selected capsules from some long-styled plants growing in 
the Botanic Gardens at Cambridge, U.S., near where plants 
of the other form grew, contained on an average 13 seeds; 
but these plants must have been subjected to unfavourable 
conditions, for some long-styled plants in a state of nature 
yielded an average of 21:5seeds per capsule. Some short-styled 
plants, which had been planted by themselves in the Botanic 
Gardens, where it was not likely that they would have been 
visited by insects that had previously visited long-styled plants, 
produced capsules, eleven of which were wholly sterile, but one 
contained 4, and another 8 seeds. So that the short-styled 
form seems to be very sterile with its own pollen. Prof. Asa 
Gray informs me that the other North American species of this 
genus are likewise heterostyled. 


OLDENLANDIA [sP.?] (RUBIACEZ). 


Mr. J. Scott sent me from India dried flowers of a hetero- 
styled species of this genus, which is closely allied to the last. 


Cuapr. III. RUBIACEA. 133 


The pistil in the long-styled flowers is longer by about a quarter 
of its length, and the stamens shorter in about the same pro- 
portion, than the corresponding organs in the short-styled 
flowers. In the latter the anthers are longer, and the divergent 
stigmas decidedly longer and apparently thinner than in the 
long-styled form. Owing to the state of the specimens, I could 
not decide whether the stigmatic papille were longer in the 
one form than in the other. The pollen-grains, distended with 
water, from the short-styled flowers were to those from the long- 
styled as 100 to 78 in diameter, as deduced from the mean of 
ten measurements of each kind. 


Hepyoris [sp. ?] (RuBrAcez). 


Fritz Miiller sent me from St. Catharina, in Brazil, dried flowers 
of a small delicate species, which grows on wet sand near the 
edges of fresh-water pools. In the long-styled form the stigma 
projects above the corolla, and stands on a level with the pro- 
jecting anthers of the short-styled form; but in the latter the 
stigmas stand rather beneath the level of the anthers in the | 
other or long-styled form, these being enclosed within the tube 
of the corolla. The pistil of the long-styled form is nearly thrice 
as long as that of the short-styled, or, speaking strictly, as 
100 to 89; and the papille on the stigma of the former are 
broader, in the ratio of 4 to 3, but whether longer than those of 
the short-styled, I could not decide. In the short-styled form, 
the anthers are rather larger, and the pollen-grains are to those 
from the long-styled flowers, as 100 to 88 in diameter. Fritz 
Miiller sent me a second, small-sized species, which is likewise 
heterostyled. 


CoccocypsELuM [spP. ?] (RUBIACEZ). 


Fritz Miiller also sent me dried flowers of this plant from 
St. Catharina, in Brazil. The exserted stigma of the long-styled 
form stands a little above the level of the exserted anthers of the 
short-styled form; and the enclosed stigma of. the latter also 
stands a little above the level of the enclosed anthers in the long- 
styledform. The pistil of the long-styled is about twice as long 
as that of the short-styled, with its two stigmas considerably 
longer, more divergent, and more curled. Fritz Miiller informs 


134  HETEROSTYLED DIMORPHIC PLANTS. Cuap. III, 


me that he could detect no difference in the size of the pollen- 
grains in the two forms. Nevertheless, there can be no doubt 
that this plant is heterostyled. 


Lirostoma [sp. ?] (RUBIAGEZR). 


Dried flowers of this plant, which grows in small wet ditches 
in St. Catharina, in Brazil, were likewise sent me by Fritz 
Miller. In the long-styled form the exserted stigma stands 
rather above the level of the exserted anthers of the other form; 
whilst in the short-styled form it stands on a level with the 
anthers of the other form. So that the want of strict corre- ~ 
spondence in height between the stigmas and anthers in the two 
forms is reversed, compared with what occurs in Hedyotis. The 
long-styled pistil is to that of the short-styled as 100 to 36 in 
length; and its divergent stigmas are longer by fully one-third 
of their own length than those of the short-styled form. In the 
latter the anthers are a little larger, and the pollen-grains are 
as 100 to 80 in diameter, compared with those from the long- 
styled form. 


CINCHONA MICRANTHA (RUBIACEZ). 


Dried specimens of both forms of this plant were sent me from 
Kew.* In the long-styled form the apex of the stigma stands 
just beneath the bases of the hairy lobes of the corolla; whilst 
the summits of the anthers are seated about halfway down 
the tube. The pistil is in length as 100 to 38 to that of the 
short-styled form. In the latter the anthers occupy the same 
position as the stigma of the other form, and they are con- 
siderably longer than those of the long-styled form. As the 
summit of the stigma in the short-styled form stands beneath 
the bases of the anthers, which are seated halfway down the 
corolla, the style has been extremely shortened in this form: 
its length to that of the long-styled being, in the specimens 
examined, only as 5:3 to 100! The stigma, also, in the short- 
styled form is very much shorter than that in the long-styled, 
in the ratio of 57 to 100. The pollen-grains from the short- 


* My attention was called to 3, given by Mr. Markham in his 
this plant by a drawing copied ‘Travels in Peru,’ p. 539. 
from Howard’s ‘ Quinologia,’ Tab, 


_ Cuap. IIL. RUBIACE. 135 


styled flowers, after having been soaked in water, were rather 
larger—in about the ratio of 100 to 91—than those from the long- 
styled flowers, and they were more triangular, with the angles 
more prominent. As all the grains from the short-styled flowers 
were thus characterised, and as they had been left in water for 
three days, I am convinced that this difference in shape in the 
two sets of grains cannot be accounted for by unequal distension 
with water. 

Besides the several Rubiaceous genera already mentioned, 
Fritz Miiller informs me that two or three species of Psychotria 
and Rudgea eriantha, natives of St. Catharina, in Brazil, are 
heterostyled, as is Manettia bicolor. I may add that I formerly 
fertilised with their own pollen several flowers on a plant of 
this latter species in my hothouse, but they did not set a single 


* fruit. From Wight and Arnott’s description, there seems to be 


little doubt that Knoxia in India is heterostyled; and Asa Gray 
is convinced that this is the case with Diodia and Spermacoce 
in the United States. Lastly, from Mr. W. W. Bailey’s descrip- 
tion,* it appears that the Mexican Bowvardia leiantha is hetero- 
styled. 


Altogether we now know of 17 heterostyled genera 
in the great family of the Rubiacee; though more 
information is necessary with respect to some of them, 
more especially those mentioned in the last para- 
graph, before we can feel absolutely safe. In the 
‘Genera Plantarum,’ by Bentham and Hooker, the 
Rubiacez are divided into 25 tribes, containing 337 
genera; and it deserves notice that the genera now 
known to be heterostyled are not grouped in one or 
two of these tribes, but are distributed in no less than 
eight of them. From this fact we may infer that 
most of the genera have acquired their heterostyled 
structure independently of one another; that is, they 


have not inherited this structure from some one or 


even two or three progenitors in common. It further 


* ‘Bull. of the Torrey Bot. Club,’ 1876, p. 106. 
cf 


1386 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IIL. 


deserves notice that in the hemostyled genera, as I 
am informed by Professor Asa Gray, the stamens are 
either exserted or are included within the tube of the 
corolla, in a nearly constant manner; so that this 
character, which is not even of specific value in the 
heterostyled species, is often of generic value in other 
members of the family. 


2 ee 


1 
. 
; 
4 


Cuap. IV. LYTHRUM SALICARIA. Ps 


CHAPTER IV. 
HETEROSTYLED TRIMORPHIC PLANTS. 


Lythrum salicaria—Description of the three forms—Their power and 
complex manner of fertilising one another—Highteen different 
unions possible—Mid-styled form eminently feminine in nature— 
Lythrum Grefferi likewise trimorphic—L. thymifolia dimorphic— 
L. hyssopifolia homostyled—Nesea verticillata trimorphic—Lager- 
streemia, nature doubtful—Oxalis, trimorphic species of—O. Valdi- 
viana—O. Regnelli, the illegitimate unions quite barren—O. spe- 
ciosa—O. sensitiva—Homostyled species of Oxalis—Pontederia, 
the one monocotyledonous genus known to include heterostyled 
species. 

Ty the previous chapters various heterostyled dimor- 
phic plants have been described, and now we come to 
heterostyled trimorphic plants, or those which present 
three forms. These have been observed in three 
families, and consist of species of Lythrum and of the 
allied genus Nesza, of Oxalis and Pontederia. In 
their manner of fertilisation these plants offer a more 
remarkable case than can be found in any other plant 
or animal. 

Lythrum salicaria.—The pistil in each form differs 
from that in either of the other forms, and in each 
there are two sets of stamens different in appearance 
and function. But one set of stamens in each form 
corresponds with a set in one of the other two forms. 
Altogether this one species includes three females or 
female organs and three sets of male organs, all as 
distinct from one another as if they belonged to dif- 
ferent species; and if smaller functional differences 


1388 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV. 


are considered, there are five distinct sets of males. 
Two of the three hermaphrodites must coexist, and 
pollen must be carried by insects reciprocally from one 
to the other, in order that either of the two should be 
fully fertile; but unless all three forms coexist, two 
sets of stamens will be wasted, and the organisation of 
the species, as a whole, will be incomplete. On the 
other hand, when all three hermaphrodites coexist, and 
pollen is carried from one to the other, the scheme 
is perfect ; there is no waste of pollen and no false co- 
adaptation. In short, nature has ordained a most com- 
plex marriage-arrangement, namely a triple union 
between three hermaphrodites,—each hermaphrodite 
being in its female organ quite distinct from the other 
two hermaphrodites and partially distinct in its male 
organs, and each furnished with two sets of males. 

The three forms may be conveniently called, from 
the unequal lengths of their pistils, the long-styled, mid- 
styled, and short-styled. The stamens also are of unequal 
lengths, and these may be called the longest, mid-length, 
and shortest. Two sets of stamens of different length are 
found in each form. The existence of the three forms 
was first observed by Vaucher,* and subsequently more 
carefully by Wirtgen; but these botanists, not being 
guided by any theory or even suspicion of their func- 
tional differences, did not perceive some of the most 
curious points of difference in their structure. I will 
first briefly describe the three forms by the aid of the 
accompanying diagram, which shows the flowers, six 
times magnified, in their natural position, with their 
petals and calyx on the near side removed. 


* ¢Hist. Phys. des Plantes und dessen Formen,” ‘ Verhand. 
d’Europe,’ tom. ii. 1841, p. 371. des naturhist. Vereins fiir preuss. 
Wirtgen,“ Ueber Lythrum salicaria Rheinl.’ 5. Jahrgang, 1848, S. 7. 


eS a a 


~ Ouar. IV. LYTHRUM SALICARIA. 139 


Fig. 10. 


'Short- 
styled. 


ue a 
\e ‘ad 


; 


Diagram of the flowers of the three forms of Lythrum salicaria, in their natural 
_ position, with the petals and calyx removed on the near side: enlarged six times. 
_ The dotted lines with the arrows show the directions in which pollen must be 
carried to each stigma to ensure full fertility. 


140 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV. 


Long-styled form.—This form can be at once recog- 
nised by the length of the pistil, which is (including 
the ovarium) fully one-third longer than that of the 
mid-styled, and more than thrice as long as that of the 
short-styled form. It is so disproportionately long, that 
it projects in the bud through the folded petals. It 
stands out considerably beyond the mid-length sta- 
mens; its terminal portion depends a little, but the 
stigma itself is shehtly upturned. The globular stigma 
is considerably larger than that of the other two forms, 
with the papille on its surface generally longer. The 
six mid-length stamens project about two-thirds the 
length of the pistil, and correspond in length with the 
pistil of the mid-styled form. Such correspondence 
in this and the two following forms is generally very 
close ; the difference, where there is any, being usually 
in a slight excess of length in the stamens. ‘The six 
shortest stamens lie concealed within the calyx; their 
ends are turned up, and they are graduated in length, 
so as to form a double row. ‘The anthers of these sta- 
mens are smaller than those of the mid-length ones. 
The pollen is of the same yellow colour in both sets. 
H. Miller* measured the pollen-grain in all three 
forms, and his measurements are evidently more trust- 
worthy than those which I formerly made, so I will 
give them. The numbers refer to divisions of the 
micrometer equalling =1, mm. The grains, distended 
with water, from the mid-length stamens are 7-73, 
and those from the shortest stamens 6-64 in diameter, 
or as 100 to 86. The capsules of this form contaim 
on an average 93 seeds: how this average was ob- 
tained will presently be explained. As these seeds, 
when cleaned, seemed larger than those from the mid- 


* «Die Befruchtung der Blumen, 1873, p. 193. 


Cuar. IV. LYTHRUM SALICARIA. 141 


styled or short-styled forms, 100 of them were placed 
in a good balance, and by the double method of weigh- 
ing were found to equal 121 seeds of the mid-styled or 
142 of the short-styled; so that five long-styled seeds 
yery nearly equal six mid-styled or seven short-styled 
seeds. 

Mid-styled form.—The pistil occupies the position 
represented in the diagram, with its extremity consi- 
derably upturned, but to a variable degree; the 
- stigma is seated between the anthers of the longest 
and the shortest stamens. The six longest stamens 
correspond in length with the pistil of the long-styled 
form; their filaments are coloured bright pink; the 
anthers are dark-coloured, but from containing bright- 
green pollen and from their early dehiscence they appear 
emerald-green. Hence in general appearance these 
stamens are remarkably dissimilar from the mid-length 
stamens of the long-styled form. The six shortest sta- 
mens are enclosed within the calyx, and resemble in 
all respects the shortest stamens of the long-styled 
form; both these sets correspond in length with the 
short pistil of the short-styled form. The green pol- 
len-grains of the longest stamens are 9-10 in dia- 
meter, whilst the yellow grains from the shortest 
stamens are only 6; or as 100 to 63. But the pollen- 
grains from different plants appeared to me, in this 
case and others, to be in some degree variable in size. 
The capsules contain on an average 130 seeds; but 
perhaps, as we shall see, this is rather too high an 
average. The seeds themselves, as before remarked, 
are smaller than those of the long-styled form. 
Short-styled form.—tThe pistil is here very short, not 
one-third of the length of that of the long-styled form. 
It is enclosed within the calyx, which, differently from 
that in the other two forms, does not enclose any an- 


142 HETEROSTYLED TRIMORPHIC PLAN'S. Cuap. IV. 


thers. The end of the pistil is generally bent upwards 
at right angles. The six longest stamens, with their 
vink filaments and green pollen, resemble the corre- 
sponding stamens of the mid-styled form. But accord- 
ing to H. Miller, their pollen-grains are a little larger, 
viz. 93-103, instead of 9-10 in diameter. ‘The six 
mid-length stamens, with their uncoloured filaments 
and yellow pollen, resemble in the size of their pollen- 
grains and in all other respects the corresponding 
stamens of the long-styled form. The difference in 
diameter between the grains from the two sets of 
anthers in the short-styled form is as 100 to 73. 
The capsules contain fewer seeds on an average than 
those of either of the preceding forms, namely 83:5; 
and the seeds are considerably smaller. In this latter 
respect, but not in number, there is a gradation 
parallel to that in the length of the pistil, the long- 
styled having the largest seeds, the mid-styled the 
next in size, and the short-styled the smallest. 

We thus see that this plant exists under three 
female forms, which differ in the length and curya- 
ture of the style, in the size and state of the stigma, 
and in the number and size of the seed. There are 
altogether thirty-six males or stamens, and these can 
be divided into three sets of a dozen each, differing 
from one another in length, curvature, and colour of 
the filaments—in the size of the anthers, and especially 
in the colour and diameter of the pollen-grains. Hach 
form bears half-a-dozen of one kind of stamens and 
half-a-dozen of another kind, but not all three kinds. 
The three kinds of stamens correspond in length with 
the three pistils: the correspondence is always between 
half of the stamens in two of the forms with the pistil 
of the third form. The following table of the diameters 
of the pollen-grains, after immersion in water, from 


Cuar. IV. LYTHRUM SALICARIA. 143 


both sets of stamens in all three forms is copied from 
H. Miller; they are arranged in the order of their 
size :— 


Pollen-grains from longest stamens of short-styled form o to 10 


= mid-styled —,, sa (9, 
+ = ”* mid- length stamens of long-styled _,, : » 7s 
8 a short-styled ,, Tauay te 
a. = shor test stamens of long-sty hetbns 2a "yt Gent 64 
” ” ” ” mid-styled » 6 » 6 


We here see that the largest pollen-grains come from 
the longest stamens, and the least from the shortest ; 
the extreme difference in diameter between them 
being as 100 to 60. 

The average number of seeds in the three forms was 


ascertained by counting them in eight fine selected 


‘capsules taken from plates growing wild, and the 
result was, as we have seen, for the long-styled (neg- 
lecting decimals) 93, mid-styled 130, and short-styled 
83. I should not have trusted in these ratios had I 
not possessed a number of plants in my garden which, 
owing to their youth, did not yield the full comple- 
ment of seed, but were of the same age and grew 
under the same conditions, and were freely visited by 
bees. I took six fine capsules from each, and found 
the average to be for the long-styled 80, for the mid- 
styled 97, and for the short-styled 61. Lastly, legiti- 
mate unions effected by me between the three forms 
gave, as may be seen in the following tables, for the 
long-styled an average of 90 seeds, for the mid-styled 
117, and for the short-styled 71. So that we have 
good concurrent evidence of a difference in the average 
production of seed by the three forms. ‘To show that 
the unions effected by me often produced their full 
effect and may be trusted, I may state that one mid- 
styled capsule yielded 151 good seeds, which is the 
same number as in the finest wild capsule which I 


144 HETEROSTYLED TRIMORPHIC PLANTS. Caap. IV. 


examined. Some artificially fertilised short- and long- 
styled capsules produced a greater number of seeds than 
was eyer observed by me in wild plants of the same 
forms, but then I did not examine many of the latter. 
This plant, I may add, offers a remarkable instance, how 
profoundly ignorant we are of the life-conditions of a 
species. Naturally it grows “in wet ditches, watery 
places, and especially on the banks of streams,” and 
though it produces so many minute seeds, it never 
spreads on the adjoining land; yet, when planted in my 
garden, on clayey soil lying over chalk, and which is so 
dry that a rush cannot be found, it thrives luxuriantly, 
grows to above 6 feet in height, produces self-sown 
seedlings, and (which is a severer test) is as fertile as 
in a state of nature. Nevertheless it would be almost 
a miracle to find this plant growing spontaneously on 
such land as that in my garden. 

According to Vaucher and Wirtgen, the three forms 
coexist in all parts of Europe. Some friends gathered 
for me in North Wales a number of twigs from 
separate plants growing near one another, and clas- 
sified them. My son did the same in Hampshire, and 
here is the result :— 


TABLE 22, 
mass | Long-styled. | Mid-styled. Short-styled. | Total. 
North Wales. . . | 95 97 72 264 
fampehire’ . .? 3) Se |S a eM ee 129 


Patel dee bban ta llseel ida” Soin ot unl | 393 


If twice or thrice the number had been collected, 
the three forms would probably have been found 
nearly equal; I infer this from considering the above 
figures, and from my son telling me that if he had 


Cuar. IV. LYTHRUM SALICARIA. 145 


collected in another spot, he felt sure that the mid- 
styled plants would have been in excess. I several 
times sowed small parcels of seed, and raised all three 
forms; but I neglected to record the parent-form, 
excepting in one instance, in which I raised from 
short-styled seed twelve plants, of which only one 
turned out long-styled, four mid-styled, and seven 
short-styled. 

Two plants of each form were protected from the 
access of insects during two successive years, and in the 
autumn they yielded very few capsules and presented 
a remarkable contrast with the adjoining uncovered 
plants, which were densely covered with capsules. In 
1865 a protected long-styled plant produced only five 
poor capsules ; two mid-styled plants produced together 
the same number ; and two short-styled plants only a 
single one. ‘These capsules contained very few seeds ; 
yet the plants were fully productive when artificially 
fertilised under the net. In a state of nature the 
flowers are incessantly visited for their nectar by hive- 
and other bees, various Diptera and Lepidoptera.* The 
nectar is secreted all round the base of the ovarium ; 
but a passage is formed along the upper and inner 
side of the flower by the lateral deflection (not repre- 
sented in the diagram) of the basal portions of the 
filaments ; so that insects invariably alight on the pro- 
jecting stamens and pistil, and insert their proboscides 
along the upper and inner margin of the corolla. We 
can now see why the ends of the stamens with their 
anthers, and the ends of the pistils with their stigmas, 


* H. Miiller givesa list of the one bee, the Cilissa melanura, 
species, ‘Die Befruchtung der almost confines its visits to this 
Blumen,’ p. 196, It appears that plant. 


146 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV. 


are a little upturned, so that they may be brushed by 
the lower hairy surfaces of the insects’ bodies. The 
shortest stamens which lie enclosed within the calyx of 
the long- and mid-styled forms can be touched only by 
the proboscis and narrow chin of a bee; hence they 
have their ends more upturned, and they are graduated 
in length, so as to fall into a narrow file, sure to be 
raked by the thin intruding proboscis. The anthers of 
the longer stamens stand laterally farther apart and are 
more nearly on the same level, for they have to brush 
against the whole breadth of the insect’s body. In 
very many other flowers the pistil, or the stamens, or 
both, are rectangularly bent to one side of the flower. 
This bending may be permanent, as with Lythrum 
and many others, or may be effected, as in Dictam- 
nus fraxinella and others, by a temporary movement, 
which occurs in the case of the stamens when the 
anthers dehisce, and in the case of the pistil when 
the stigma is mature; but these two movements do 
not always take place simultaneously in the same 
flower, Now I have found no exception to the rule, 
that when the stamens and pistil are bent, they bend 
to that side of the flower which secretes nectar, even 
though there be a rudimentary nectary of large size 
on the opposite side, as in some species of Corydalis. 
When nectar is secreted on all sides, they bend to 
that side where the structure of the flower allows the 
easiest access to it, as in Lythrum, various Papilio- 
nacew, and others. The rule consequently is, that 
when the pistils and stamens are curved or bent, the 
stigma and anthers are thus brought into the path- 
way leading to the nectary. ‘There are a few cases 
which seem to be exceptions to this rule, but they are 
not so in truth; for instance, in the Gloriosa lily, the 
stigma of the grotesque and rectangularly bent pistil 


- 


Cuar. IV. LYTHRUM SALICARIA. 147 


is brought, not into any pathway from the outside 
towards the nectar-secreting recesses of the flower, but 
into the circular route which insects follow in proceed- 
ing from one nectary to the other. In Scrophularia 
aquatica the pistil is bent downwards from the mouth 
of the corolla, but it thus strikes the pollen-dusted 
breast of the wasps which habitually visit these ill- 
scented flowers. In all these cases we see the supreme 
dominating power of insects on the structure of flowers, 
especially of those which have irregular corollas. 
Flowers which are fertilised by the wind must of 
course be excepted; but I do not know of a single 
instance of an irregular flower which is thus fertilised. 

Another point deserves notice. In each of the three 
forms two sets of stamens correspond in length with 
the pistils in the other two forms. When bees suck the 
flowers, the anthers of the longest stamens, bearing the 
green pollen, are rubbed against the abdomen and the 
inner sides of the hind legs, as is hkewise the stigma of 
the long-styled form. The anthers of the mid-length 
stamens and the stigma of the mid-styled form are 
rubbed against the under side of the thorax and be- 
tween the front pair of legs. And, lastly, the anthers 
of the shortest stamens and the stigma of the short- 
styled form are rubbed against the proboscis and chin ; 
for the bees in sucking the flowers insert only the front 
part of their heads into the flower. On catching bees, I 
observed much green pollen on the inner sides of the 
hind legs and on the abdomen, and much yellow 
pollen on the under side of the thorax. There was 
also pollen on the chin, and, it may be presumed, on 
the proboscis, but this was difficult to observe. I had, 
however, independent proof that pollen is carried on 
the proboscis ; for a small branch of a protected short- 
styled plant (which produced spontaneously only two 


148 HETEROSTYLED TRIMORPHIC PLANTS. Cuapr. TV. 


capsules) was accidentally left during several days 
pressing against the net, and bees were seen inserting 
their proboscides through the meshes, and in conse- 
quence numerous capsules were formed on this one 
small branch. From these several facts it follows that 
insects will generally carry the pollen of each form from 
the stamens to the pistil of corresponding length; and 
we shall presently see the importance of this adapta- 
tion. It must not, however, be supposed that the bees 
do not get more or less dusted all over with the several 
kinds of pollen; for this could be seen to oceur with 
the green pollen from the longest stamens. Moreover 
a case will presently be given of a long-styled plant 
producing an abundance of capsules, though grow- 
ing quite by itself, and the flowers must have been 
fertilised by their own two kinds of pollen; but 
these capsules contained a very poor average of seed. 
Hence insects, and chiefly bees, act both as general 
carriers of pollen, and as special carriers of the right 
sort. 

Wirtgen remarks* on the variability of this plant in 
the branching of the stem, in the length of the bractez, 
size of the petals, and in several other characters. The 
plants which grew in my garden had their leaves, 
which differed much in shape, arranged oppositely, 
alternately, or in whorls of three. In this latter case 
the stems were hexagonal; those of the other plants 
being quadrangular. But we are concerned chiefly, 
with the reproductive organs: the upward bending of 
the pistil is variable, and especially in the short-styled 
form, in which it is sometimes straight, sometimes 
slightly curved, but generally bent at right angles. 


* ¢Verhand. des naturhist. Vereins, fiir Pr. Rheinl’ 5. Jahrgang 
1848, pp. 11, 13. 


Cuar. IV. LYTHRUM SALICARIA. 149 


longer papille or is rougher than that of the mid- 
styled, and the latter than that of the short-styled ; 
but this character, though fixed and uniform in the 
two forms of Primula veris, &c., is here variable, for 
I have seen mid-styled stigmas rougher than those 
of the long-styled.* The degree to which the longest 
and mid-leneth stamens are graduated in length and 
have their ends upturned is variable; sometimes all 
are equally long. The colour of the green pollen in 
the longest stamens is variable, being sometimes pale 
greenish-yellow ; in one short-styled plant it was almost 
white. The grains vary a little in size: I examined 
one short-styled plant with the grains above the 
average size; and I have seen a long-styled plant with 
the grains from the mid-length and shortest anthers of 
the same size. We here see great variability in many 
important characters; and if any of these variations 
were of service to the plant, or were correlated with 
useful functional differences, the species is in that 
state in which natural selection might readily do much 
for its modification. 


On the Power of Mutual Fertilisation between the three 
Forms. 


Nothing shows more clearly the extraordinary com- 
plexity of the reproductive system of this plant, than 
the necessity of making eighteen distinct unions in 
order to ascertain the relative fertilising power of the 


* The plants which I observed 
grew in my garden, and probably 
varied rather more than those 
growing in a state of nature. H. 
Miiller has described the stigmas 
of all three forms with great care, 


and he appears to have found the 
stigmatic papille differing con- 
stantly in length and structure in 
the three forms, being longest in 
the long-styled form, 


150 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV, 


three forms. Thus the long-styled form has to be fer- 
tilised with pollen from its own two kinds of anthers, 
from the two in the mid-styled, and from the two in 
the short-styled form. The same process has to be 
repeated with the mid-styled and short-styled forms. 
It might have been thought sufficient to have tried on 
each stigma the green pollen, for instance, from either 
the mid- or short-styled longest stamens, and not 
from both; but the result proves that this would 
have been insufficient, and that it was necessary to 
try all six kinds of pollen on each stigma. As in 
fertilismg flowers there will always be some failures, 
it would have been advisable to have repeated each of 
the eighteen unions a score of times; but the labour 
would have been too great; as it was, 1 made 223 
unions, i.e. on an average I fertilised above a dozen 
flowers in the eighteen different methods. Hach flower 
was castrated ; the adjoining buds had to be removed, 
so that the flowers might be safely marked with 
thread, wool, &c.; and after each fertilisation the stigma 
was examined with a lens to see that there was suffi- 
cient pollen on it. Plants of all three forms were 
protected during two years by large nets on a frame- 
work ; two plants were used during one or both years, 
in order to avoid any individual peculiarity in a par- 
ticular plant. As soon as the flowers had withered, 
the nets were removed; and in the autumn the cap- 
sules were daily inspected and gathered, the ripe 
seeds being counted under the microscope. I have 
given these details that confidence may be placed 
in the following tables, and as some excuse for two 
blunders which, I beiieve, were made. These blunders 
are referred to, with their probable cause, in two 
foot-notes to the tables. The erroneous numbers, how- 
ever, are entered in the tables, that it may not be sup- 


- 
_ 
P 


Bi a a Ril eb i i Ae. 


Cuar. IV. LYTHRUM SALICARIA. 151 


posed that I have in any one instance tampered with 
the results. 

A few words explanatory of the three tables must be 
given. Each is devoted to one of the three forms, and 
is divided into six compartments. The two upper ones 
in each table show the number of good seeds resulting 
from the application to the stigma of pollen from the 
two sets of stamens which correspond in length with 
the pistil of that form, and which are borne by the 
other two forms. Such unions are of a legitimate 
nature. The two next lower compartments show the 
result of the application of pollen from the two sets of 
stamens, not corresponding in length with the pistil, 
and which are borne by the other two forms. These 
unions are illegitimate. The two lowest compartments 
show the result of the application of each form’s own 
two kinds of pollen from the two sets of stamens be- 
longing to the same form, and which do not equal the 
pistil in length. These unions are likewise illegiti- 
mate. The term own-form pollen here used does not 
mean pollen from the flower to be fertilised—for this 
was never used—but from another flower on the same 
plant, or more commonly from a distinct plant of the 
same form. The figure (0) means that no capsule was 
produced, or if a capsule was produced that it contained 
no good seed. In some part of each row of figures in 
each compartment, a short horizontal line may be seen ; 
the unions above this line were made in 1862, oa 
below it in 1863. It is of importance to observe this, 
as it shows that the same general result was obtained 
during two successive years; but more especially be- 
cause 1863 was a very hot and dry season, and the 
plants had occasionally to be watered. This did not pre- 
vent the full complement of seed being produced from 
the more fertile unions; but it rendered the less fertile 


152 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV 


ones even more sterile than they otherwise would have 
been. I have seen striking instances of this fact in 
making illegitimate and legitimate unions with Pri- 
mula; and it is well known that the conditions of life 
must be highly favourable to give any chance of suc- 
cess in producing hybrids between species which are 


crossed with difficulty. 


TABLE 23.—Long-styled Form. 


IE 
Legitimate union. 

13 flowers fertilised by the longest 
stamens of the mid-styled. These 
stamens equal in length the pistil 
of the long-styled. 


Product of good seed in each cap- 
sule. 

36 dE 

81 

0 

0 

0 

45 

41 

38 per cent. of these flowers 

yielded capsules. Each capsule con- 
tained, on an average, 51°2 seeds. 


Oo 


oooccoo 


IL. 
Illegitimate union. 


14 flowers fertilised by the short- 
est stamens of the mid-styled. 


oo | ooocu 
ooococoo 


Too sterile for any average. 


II. 
Legitimate union. 

13 flowers fertilised by the longest 
stamens of the short-styled. ‘These 
stamens equal in length the pistil 
of the long-styled. 


Product of good seed in each cap- 


sule. 

159 104 
43 119 
96 poor seed. 96 

103 99 

0 131 
0) 116 


114 
84 per cent. of these flowers 


yielded capsules, Each capsule con- 
tained, on an average, 107°3 seeds. 


ive 
Illegitimate union. 
12 flowers fertilised by the mid- 
length stamens of the short-styled. 


20 0 
0 0 
0 0 
0 10) 
= 0 
0 0 
0 


Too sterile for any average. 


Cuar. IV. LYTHRUM SALICARLA. 153 
TABLE 23.—Long-styled Form—continued. 


Wie vials 

Illegitimate union. Illegitimate union. 

15 flowers fertilised by own-form 15 flowers fertilised by own-form 
mid-length stamens. shortest stamens. 

2 
10 
23 
0 
0 
0 
0 
0 


Too sterile for any average. Too sterile for any average. 


Sooocoe!| 
ocoooocooror 
ooccooe! 


Besides the aboye experiments, I fertilised a consi- 
derable number of long-styled flowers with pollen, 
taken by a camel’s-hair brush, from both the mid- 
length and shortest stamens of their own form: only 
5 capsules were produced, and these yielded on an 
average 14°5 seeds. In 1865 I tried a much better ex- 
periment: a long-styled plant was grown by itself, 
miles away from any other plant, so that the flowers 
could have received only their own two kinds of pol- 
len. The flowers were incessantly visited by bees, and 
their stigmas must have received successive applica- 
tions of pollen on the most favourable days and at the 
most favourable hours: all who have crossed plants 
know that this highly favours fertilisation. This plant 
produced an abundant crop of capsules; I took by 
chance 20 capsules, and these contained seeds in 
number as follows :— 


20 20 35 21 19 
26 24 12 23 10 

7 30 27 29 . 13 
20 12 29 19 35 


154 HETEROSTYLED TRIMORPHIC PLANTS. Cuapr. LY. 


This gives an average of 21°5 seeds per capsule. As 
we know that the long-styled form, when standing 
near plants of the other two forms and fertilised by 
insects, produces on an average 93 seeds per capsule, 
we see that this form, fertilised by its own two pollens, 


yields only between one-fourth and one-fifth of the full. 


number of seed. I have spoken as if the plant had re- 
ceived both its own kinds of pollen, and this is, of 


course, possible ; but, from the enclosed position of the | 


shortest stamens, it is much more probable that the 
stigma received exclusively pollen from the mid- 
length stamens; and this, as may be seen in com- 
partment V. in Table 23, is the more fertile of the two 
self-unions. 


TABLE 24.—WMid-styled Form. 


1. | Il. 


Legitimate wnion. | Legitimate union. 
| 
12 flowers fertilised by the mid- | 12 flowers fertilised by the mid- 


length stamens of the long-styled. | length stamens of the short-styled. 
These stamens equal in length the | These stamens equal in length the 


pistil of the mid-styled. pistil of the mid-styled. 
Product of good seed in each cap- Product of good seed in each cap- 
sule. sule, 

138 122 112 109 

149 50 150 143 

147 151 | 143 124 

109 119 100 145 

133 138 33 12 

144 0 _— 141 

— 104 

92 per cent. of the flowers (pro- | 100 per cent. of the towers yieldel 


bably 100 per cent.) yielded cap- capsules. Each capsule’ contained, 

sules. Each capsule contained, on | on an average, 108°0 seeds; or, ex- 

an average, 127 3 seeds. cluding capsules with less than 20 
F | seeds, the average is 116°7 seeds. 


RRR 


ae 


: 
P 
; 
4 


Cuapr. IV. 


LYTHRUM SALICARIA. 


155 


TABLE 24.— Mid-styled Form—continued. 


IIL. 

a Illegitimate union. 

13 flowers fertilised by the short- 
est stamens of the long-styled. 


83 12 
0 19 
- {seeds small 
: 85{ and poor. 
44 0 
44 0 
45 0 


capsules. Each capsule contained, 
on an average, 47°4 seeds; or, ex- 
cluding capsules with less than 20 
seeds, the average is 60-2 seeds. 


Vic 
Illegitimate union. 
12 flowers fertilised by own-form 
longest stamens. 


92 0 
3) 0 
63 0 
— 0 
136?* 0 
0 0 

0 


20 seeds, the average is 77°5. 


54 per cent. of the flowers yielded | 


IY, 
Illegitimate union. 


15 flowers fertilised by the long 
est stamens of the short-styled. 


150 86 
115 115 
14 29 
6 17 

2 113 

9 79 
— 128 
132 0 


93 per cent. of the flowers yielded 
capsules. Each capsule contained, 
on an average, 69°5 seeds; or, ex- 
cluding capsules with less than 20 
seeds, the average is 102°8. 


VEE 
Illegitimate union. 
12 flowers fertilised by own-form 


| shortest stamens. 


Excluding the capsule with 136 | 
- seeds, 25 per cent. of the flowers | 
yielded capsules, and each capsule | 
contained, on an average, 54°6 seeds; | 
or, excluding capsules with lessthan | 


coool ooo 
ooococoo 


Not one flower yielded a capsule. 


* I have hardly a doubt that 
this result of 136 seeds in compart- 
ment V. was due to a gross error. 
The flowers to be fertilised by 
their own longest stamens were 
first marked by “ white thread,” 
and those by the mid-lenzth 
stamens of the long-styled form 
by “white silk ;” a flower fertilised 
in the later manner would have 
_ yielded about 136 seeds, and it may 
be observed that one such pod is 


missing, viz. at the bottom of 
compartmentI. Therefore I have 
hardly any doubt that I fertilised 
a flower marked with “ white 
thread”’ as if it had been marked 
with “ white silk.” With respect 
to the capsule which yielded 92 
seeds, in the same column with 
that which yielded 136, I do 
not know what to think. I 
endeavoured to prevent pollen 
dropping from an upper to a lower 


156 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV. 

Besides the experiments in the above table, I ferti- 
lised a considerable number of mid-styled flowers with 
pollen, taken by a camel’s-hair brush, from both the 
longest and shortest stamens of their own form: only 
5 capsules were produced, and these yielded on an 
average 11-0 seeds. 


TABLE 25.—Short-styled Form. 


I 
Legitimate union. 
12 flowers fertilised by the short- 
est stamens of the long-styled. 


These stamens equal in length the 
pistil of the short-styled. 


69 56 
61 88 
88 112 
66 111 
0 62 
0 100 


83 per cent. of the flowers yielded 
capsules. Each capsule contained, 
on an average, 81-3 seeds. 


Ill. 
Illegitimate union. 
10 flowers fertilised by the mid- 
length stamens of the long-styled, 


0 14 

0 0 

0 0 

0 0 
- 0 
23 


Too sterile for any average. 


Il. 
Legitimate wnion. 

13 flowers fertilised by the short- 
est stamens of the mid-styled. 
These stamens equal in length the 
pistil of the short-styled. 


93 69 
77 69 
48 53 
43 9 
0 0 
0 0 


0 
61 per cent. of the flowers yielded 
capsules. Each capsule contained, 
on an average, 64°6 seeds. 


IV, 
Illegitimate union. 


10 flowers fertilised by the long- 
est stamens of the mid-styled. 


0 0 
0 0 
0 0 
0 0 
—_ 0 
0 


Too sterile for any average. 


flower, and I tried to remember to 
wipe the pincers carefully after 
each fertilisation; but in making 
eighteen different unions, some- 
times on windy days, and pestered 
by bees and flies buzzing about, 
some few errors could hardly be 
avoided. One day I had to keep 
a third man by me all the time to 
prevent the bees visiting the un- 


covered plants, for in a few 
seconds’ time they might have 
done irreparable mischief. It was 
also extremely difficult to exclude 
minute Diptera from the net. In 
1862 I made the great mistake of 
placing a mid-styled and long- 
styled under the same huge net : 
in 1863 I avoided this error, 


Cuar. IV. LYTHRUM SALICARIA. 157 


TABLE 25.—Short-styled Form—continued. 


v. VI. 
Illegitimate union. Illegitimate union. 
10 flowers fertilised by own-form 10 flowers fertilised by own-form 
longest stamens. mid-iength stamens. 
0 0 642* 0 
0 0 0 0 
0 0 ) 0) 
= 0 a 0 
0 0 21 0 
0 9 
Too sterile for any average. Too sterile for any average. 


Besides the experiments in the table, I fertilised a 
number of flowers without particular care with their 
own two kinds of polleh, but they did not produce a 
single capsule. 


Summary of the Results. 


_ Long-styled form.—Twenty-six flowers fertilised le- 
gitimately by the stamens of corresponding length, 
borne by the mid- and short-styled forms, yielded 61°5 
per cent. of capsules, which contained on an average 
89°7 seeds. 

Twenty-six long-styled flowers fertilised illegiti- 
mately by the other stamens of the mid- and short- 
styled forms yielded only two very poor capsules. 

Thirty long-styled flowers fertilised illegitimately by 
their own-form two sets of stamens yielded only eight 
very poor capsules; but long-styled flowers fertilised 


* I suspect that by mistake I to be thus fertilised were marked 
fertilised this flower in compart- with black silk; those with pollen 
ment VI. with pollen from the from the mid-length stamens of 
shortest stamens of thelong-styled _ the short-styled with black thread; 
form, and it would then have and thus probably the mistake 
yielded about G4 seeds. Flowers arose. 


158 HETEROSTYLED TRIMORPHIC PLANTS. Cnap. IV. 


by bees with pollen from their own stamens produced 
numerous capsules containing on an average 21°5 
seeds. 

Mid-styled form.—Twenty-four flowers legitimately 
fertilised by the stamens of corresponding length, 
borne by the long and short-styled forms, yielded 96 
(probably 100) per cent. of capsules, which contained 
(excluding one capsule with 12 seeds) on an average 
117-2 seeds. 

Fifteen mid-styled flowers fertilised illegitimately 
by the longest stamens of the short-styled form yielded 
93 per cent. of capsules, which (excluding four cap- 
sules with less than 20 seeds) contained on an average 
102°8 seeds. I 

Thirteen mid-styled flowers fertilised legitimately 
by the mid-length stamens of the long-styled form 
yielded 54 per cent. of capsules, which (excluding 
one with 19 seeds) contained on an average 60:2 seeds. 

Twelve mid-styled flowers fertilised illegitimately 
by their own-form longest stamens yielded 25 per 
cent. of capsules, which (excluding one with 9 seeds) 
contained on an average 77°50 seeds. 

Twelve mid-styled flowers fertilised illegitimately 
by their own-form shortest stamens yielded not a 
single capsule. 

Short-styled form.—Twenty-five flowers fertilised 
legitimately by the stamens of corresponding length, 
borne by the long and mid-styled forms, yielded 72 
per cent. of capsules, which (excluding one capsule 
with only 9 seeds) contained on an average 70°8 
seeds. 

Twenty short-styled flowers fertilised illegitimately 
by the other stamens of the long and mid-styled forms 
yielded only two very poor capsules. 

Twenty short-styled flowers fertilised illegitimately 


Cuar. IV. © LYTHRUM SALICARIA. 159 


by their own stamens yielded only two poor (or per- 
haps three) capsules. 

If we take all six legitimate unions together, and 
all twelve illegitimate unions together, we get the fol- 
lowing results :— 


TABLE 26. 
j | a s Average 
, Number Number Wanteee cf Number of 
Nature of Union. | of Flowers | of Capsules Saadaune Seeds per 
fertilised. produced. ie : Flower fer- 
ee tilised. 
1. | | 
The six legitimate 75 56 96-29 71°39 
unions , = | 
eee ee 4s | ae | 44-72 | 11°03 


| i 
} 


Therefore the fertility of the legitimate unions to that 
of the illegitimate, as judged by the proportion of the 
fertilised flowers which yielded capsules, is as 100 to 
33; and judged by the average number of seeds per 
capsule, as 100 to 46. 

From this summary and the several foregoing tables 
we see that it is only pollen from the longest stamens 
which can fully fertilise the longest pistil; only that 
from the mid-length stamens, the mid-length pistil; 
and only that from the shortest stamens, the shortest 
pistil. And now we can comprehend the meaning of 
the almost exact correspondence in length between 
the pistil in each form and a set of six stamens 
in two of the other forms; for the stigma of each 
form is thus rubbed against that part of the insect’s 
body which becomes charged with the proper pollen. 
It is also evident that the stigma of each form, 
fertilised in three different ways with pollen from 
the longest, mid-length, and shortest stamens, is acted 
on very differently, and conversely that the pollen from 

8 


160 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV. 


the twelve longest, twelve mid-length, and twelve 
shortest stamens acts very differently on each of the 
three stigmas; so that there are three sets of female 
and of male organs. Moreover, in most cases the six 
stamens of each set differ somewhat in their fertilising 
power from the six corresponding ones in one of the 
other forms. We may further draw the remarkable 
conclusion that the greater the inequality in length 
between the pistil and the set of stamens, the pollen 
of which is employed for its fertilisation, by so much 
is the sterility of the union increased. There are no 
exceptions to this rule. To understand what follows 
the reader should look to Tables 23, 24, and 25, and 
to the diagram Fig. 10, p. 139. In the long-styled form 
the shortest stamens obviously differ in length from 
the pistil to a greater degree than do the mid-length 
stamens; and the capsules produced by the use of 
pollen from the shortest stamens contain fewer seeds 
than those produced by the pollen from the mid- 
length stamens. The same result follows with the 
long-styled form, from the use of the pollen of the 
shortest stamens of the mid-styled form and of the 
mid-length stamens of the short-styled form. The 
same rule also holds good with the mid-styled and 
short-styled forms, when illegitimately fertilised with 
pollen from the stamens more or less unequal in 
length to their pistils. Certainly the difference in 
sterility in these several cases is slight; but, as far as 
we are enabled to judge, it always increases with the 
increasing inequality of length between the pistil and 
the stamens which are used in each case. 

The correspondence in length between the pistil in 
each form and a set of stamens in the other two forms, 
is probably the direct result of adaptation, as it is of 
high service to the species by leading to full and 


— Ae,° ee 


Cuar. IV. LYTHRUM SALICARIA. 161 


legitimate fertilisation. But the rule of the increased 
sterility of the illegitimate unions according to the 
greater inequality in length between the pistils and 
stamens employed for the union can be of no service. 
With some heterostyled dimorphic plants the dif- 
ference of fertility between the two illegitimate unions 
appears at first sight to be related to the facility of 
self-fertilisation ; so that when from the position of 
the parts the liability in one form to self-fertilisation 
is greater than in the other, a union of this kind 
has been checked by having been rendered the 
more sterile of the two. But this explanation does 
not apply to Lythrum; thus the stigma of the long- 
styled form is more liable to be illegitimately fer- 
tilised with pollen from its own mid-length stamens, 
or with pollen from the mid-length stamens of the 
short-styled form, than by its own shortest stamens 
or those of the mid-styled form; yet the two former 
unions, which it might have been expected would 
have been guarded against by increased sterility, 
are much less sterile than the other two unions 
which are much less likely to be effected. The 
same relation holds good even in a more striking 
manner with the mid-styled form, and with the short- 
styled form as far as the extreme sterility of all its 
illegitimate unions allows of any comparison. We 
are led, therefore, to conclude that the rule of in- 
creased sterility in accordance with increased in- 
equality in length between the pistils and stamens, 
is a purposeless result, incidental on those changes 
through which the species has passed in acquiring 
certain characters fitted to ensure the legitimate 
fertilisation of the three forms. 

Another conclusion which may be drawn from 
Tables 23, 24, and 25, even from a glance at them, 


162 HETEROSTYLED TRIMORPHIC PLANTS. Cap. IV. 


is that the mid-styled form differs from both the 
others in its much higher capacity for fertilisation 
in various ways. Not only did the twenty-four flowers 
legitimately fertilised by the stamens of corresponding 
lengths, all, or all but one, yield capsules rich in 
seed; but of the other four illegitimate unions, that 
by the longest stamens of the short-styled form was 
highly fertile, though less so than the two legitimate 
unions, and that by the mid-length stamens of the 
long-styled form was fertile to a considerable degree ; 
the remaining two illegitimate unions, namely, with 
this form’s own pollen, were sterile, but in different 
degrees. So that the mid-styled form, when fertilised 
in the six different possible methods, evinces five 
grades of fertility. By comparing compartments III. 
and VI. in Table 24 we may see that the action of 
the pollen from the shortest stamens of the long-styled 
and mid-styled forms is widely different; in the one 
case above half the fertilised flowers yielded capsules 
containing a fair number of seeds; in the other case 
not one capsule was produced. So, again, the green, 
large-grained pollen from the longest stamens of 
the short-styled and mid-styled forms (in compart- 
ments iY. and V.) is widely different. In both these 
cases the difference in action is so plain that it cannot 
be mistaken, but it can be corroborated. If we look 
to Table 25 to the legitimate action of the shortest 
stamens of the long- and mid-styled forms on the 
short-styled form, we again see a similar but slighter 
difference, the pollen of the shortest stamens of the 
mid-styled form yielding a smaller average of seed 
during the two years of 1862 and 1863 than that from 
the shortest stamens of the long-styled form. Again, 
if we look to Table 23, to the legitimate action on 
the long-styled form of the green pollen of the two 


Cuap. IV. LYTHRUM SALICARIA. 163 


sets of longest stamens, we shall find exactly the same 
result, viz. that the pollen from the longest stamens of 
the mid-styled form yielded during both years fewer 
seeds than that from the longest stamens of the 
short-styled form. Hence it is certain that the two 
kinds of pollen produced by the mid-styled form are 
less potent than the two similar kinds of pollen pro- 
duced by the corresponding stamens of the other two 
forms. 

In close connection with the lesser potency of the 
two kinds of pollen of the mid-styled form is the fact 
that, according to H. Miller, the grains of both are 
a little less in diameter than the corresponding grains 
produced by the other two forms. Thus the grains 
from the longest stamens of the mid-styled form are 
9 to 10, whilst those from the corresponding stamens 
of the short-styled form are 94 to 10} in diameter. 
So, again, the grains from the shortest stamens of the 
mid-styled are 6, whilst those from the corresponding 
stamens of the long-styled are 6 to 64 in diameter. 
It would thus appear as if the male organs of the 
mid-styled form, though not as yet rudimentary, were 
tending in this direction. On the other hand, the 
female organs of this form are in an eminently efficient 
state, for the naturally fertilised capsules yielded a 
considerably larger average number of seeds than 
those of the other two forms—almost every flower 
which was artificially fertilised in a legitimate manner 
produced a capsule—and most of the illegitimate 
unions were highly productive. The mid-styled form 
thus appears to be highly feminine in nature; and al- 
though, as just remarked, it is impossible to consider 
its two well-developed sets of stamens which produce 
an abundance of pollen as being in a rudimentary 
condition, yet we can hardly ayoid connecting as 


164. HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV. 


balanced the higher efficiency of the female organs 
in this. form with the lesser efficiency and lesser size 
of its two kinds of pollen-grains. The whole case 
appears to me a very curious one. 

It may be observed in Tables 23° to 25 that some 
of the illegitimate unions yielded during neither year 
a single seed ; but, judging from the long-styled plants, 
it is probable, if such unions were to be effected re- 
peatedly by the aid of insects under the most fayour- 
able conditions, some few seeds would be produced in 
every case. Anyhow, it is certain that in all twelve 
illegitimate unions the pollen-tubes penetrated the 
stigma in the course of eighteen hours. At first I 
thought that two kinds of pollen placed together on 
the same stigma would perhaps yield more seed than 
one kind by itself; but we have seen that this is not 
so with each form’s own two kinds of pollen; nor is it 
probable in any case, as I occasionally got, by the use 
of a single kind of pollen, fully as many seeds as a 
capsule naturally fertilised ever produces. Moreover 
the pollen from a single-anther is far more than suffi- 
cient to fertilise fully a stigma; hence, in this as with 
so many other plants, more than twelve times as much 
of each kind of pollen is produced as is necessary to 
ensure the full fertilisation of each form. From the 
dusted condition of the bodies of the bees which I 
caught on the flowers, it is probable that pollen of 
various kinds is often deposited on all three stigmas ; 
but from the facts already given with respect to 
the two forms of Primula, there can hardly be a 
doubt that pollen from the stamens of corresponding 
length placed on a stigma would be prepotent over 
any other kind of pollen and obliterate its effects, 
—even if the latter had been placed on the stigma 
some hours previously. 


| 
| 
| 


Cuar. IV. LYTHRUM GRZFFERI. °- 165 


Finally, it has now been shown that Lythrum salicaria 
presents the extraordinary case of the same species 
bearing three females, different in structure and func- 
tion, and three or even five sets (if minor differences 
are considered) of males; each set consisting of half- 
a-dozen, which likewise differ from one another in 
structure and function. 


Lythrum GrefferiiI have examined numerous dried flowers 
of this species, each from a separate plant, sent me from Kew. 
Like Z. salicaria, it is trimorphic, and the three forms appa- 
rently occur in about equal numbers. In the long-styled form 
the pistil projects about one-third of the length of the calyx 
beyond its mouth, and is therefore relatively much shorter than 
in L. salicaria ; the globose and hirsute stigma is larger than 
that of the other two forms; the six mid-length stamens, which 
are graduated in length, have their anthers standing close above 
and close beneath the mouth of the calyx; the six shortest 
stamens rise rather above the middle of the calyx. In the mid- 
styled form the stigma projects just above the mouth of the 
calyx, and stands almost on a level with the mid-length stamens 
of the long and short-styled forms; its own longest stamens 
project well above the mouth of the calyx, and stand a little 
above the level of the stigma of the long-styled form. In short, 
without ‘entering on further details, there is a close general 
correspondence in structure between this species and ZL. salicaria, 
but with some differences in the proportional lengths of the 


_ parts. The fact of each of the three pistils having two sets of 


stamens of corresponding lengths, borne by the two other forms, 


* eomes out conspicuously. In the mid-styled form the pollen- 


grains from the longest stamens are nearly double the diameter 
of those from the shortest stamens; so that there is a greater 
difference in this respect than in L. salicaria. In the long- 
styled form, also, the difference in diameter between the pollen- 
grains of the mid-length and shortest stamens is greater than 
in L. salicaria. These comparisons, however, must be received 
with caution, as they were made on specimens soaked in water 
after having been long kept dry. 

Lythrum thymifolia.—This form, according to Vaucher,* is 


* ‘Hist. Phys. des Plantes d’Europe,’ tom. ii. (1841), pp. 369, 371. 


166 HETEROSTYLED TRIMORPHIC PLANTS. Cuapr. IV. 


dimorphic, like Primula, and therefore presents only two forms. 
I received two dried flowers from Kew, which consisted of the 
two forms; in one the stigma projected far beyond the calyx, in 
the other it was included within the calyx; in this latter form 
the style was only one-fourth of the length of that in the other 
form. There are only six stamens; these are somewhat gradu- 
ated in length, and their anthers in the short-styled form stand 
a little above the stigma, but yet by no means equal in length 
the pistil of the long-styled form. In the latter the stamens 
are rather shorter than those in the other form. The six 
stamens alternate with the petals, and therefore correspond 
homologically with the longest stamens of J. salicaria and L. 
Grefferi. 

Lythrum hyssopifolia.—This species is said by Vaucher, but I 
believe erroneously, to be dimorphic. I have examined dried 
flowers from twenty-two separate plants from various localities, 
sent tome by Mr. Hewett C. Watson, Professor Babington, and 
others. These were all essentially alike, so that the species 
cannot be heterostyled. The pistil varies somewhat in length, 
but when unusually long, the stamens are likewise generally 
long; in the bud the stamens are short; and Vaucher was 
perhaps thus deceived. There are from six to nine stamens, 
graduated in length. The three stamens, which vary in being 
either present or absent, correspond with the six shorter stamens 
of LZ. salicaria and with the six which are always absent in LZ. 
thymifolia. The stigma is included within the calyx, and stands 
in the midst of the anthers, and would generally be fertilised 
by them; but as the stigma and anthers are upturned, and as, 
according to Vaucher, there is a passage left in the upper side 
of the flower to the nectary, there can hardly be a doubt that 
the flowers are visited by insects, and would occasionally be 
cross-fertilised by them, as surely as the flowers of the short- 
styled L. salicaria, the pistil of which and the corresponding 
stamens in the other two forms closely resemble those of L. hys- 
sopifolia. According to Vaucher and Lecoq,* this species, which 
is an annual, generally grows almost solitarily, whereas the 
three preceding species are social; and this fact alone would 
almost haye convinced me that L. hyssopifolia was not hetero- 
styled, as such plants cannot habitually live isolated any better 
than one sex of a dicecious species. 


* ¢Géograph. Bot. de Europe,’ tom. vi. 1857, p. 157. 


y— = * 


| 


_ Cuar. IV LAGERSTRGEMIA INDICA. 167 


We thus see that within this genus some species are hetero- 
styled and trimorphic; one apparently heterostyled and dimor- 
phic, and one homostyled. 

Nesea verticillata—I raised a number of plants from seed 
sent me by Professor Asa Gray, and they presented three forms. 
These differed from one another in the proportional lengths of 
their organs of fructification and in all respects, in very nearly 
the same way as the three forms of Lythrum Grefferi. The 
green pollen-grains from the longest stamens, measured along 
their longer axis and not distended with water, were ;}3, of an 


inch in length; those from the mid-length stamens —, and 


those from the shortest stamens pea of an inch. So that the 
largest pollen-grains are to the smallest in diameter as 100 to 
65. This plant inhabits swampy ground in the United States. 
According to Fritz Miiller,* a species of this genus in St. Catha- 
rina, in Southern Brazil, is homostyled. 

Lagerstremia Indica.—This plant, a member of the Lythracez, 
may perhaps be heterostyled, or may formerly have been so. It 
is remarkable from the extreme variability of its stamens. On 
a plant, growing in my hothouse, the flowers included from 
nineteen to twenty-nine short stamens with yellow pollen, 
which correspond in position with the shortest stamens of 
Lythrum; and from one to five (the latter number being the 
commonest) very long stamens, with thick flesh-coloured fila- 
ments and green pollen, corresponding in position with the 
longest stamens of Lythrum. In one flower, two of the long 
stamens produced green, while a third produced yellow pollen, 
although the filaments of all three were thick and flesh-coloured. 
In an anther of another flower, one cell contained green and 
the other yellow pollen. The green and yellow pollen-grains 
from the stamens of different length are of the same size. 
The pistil is a little bowed upwards, with the stigma seated 
between the anthers of the short and long stamens, so that 
this plant was mid-styled. Eight flowers were fertilised with’ 
green pollen, and six with yellow pollen, but not one set fruit. 
This latter fact by no means proves that the plant is hetero- 
styled, as it may belong to the class of self-sterile species. 
Another plant growing in the Botanic Gardens at Calcutta, as 
Mr. J. Scott informs me, was long-styled, and it was equally 


* ‘Bot. Zeitung,’ 1868, p. 112. 


168 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV. 


sterile with its own pollen; whilst a long-styled plant of 
L. regine, though growing by itself, produced fruit. I examined 
dried flowers from two plants of L. parviflora, both of which 
were long-styled, and they differed from ZL. Jndica in having 
eight long stamens with thick filaments, and a crowd of shorter 
stamens. Thus the evidence whether L. Jndica is hetero- 
styled is curiously conflicting: the unequal number of the short 
and long stamens, their extreme variability, and especially the 
fact of their pollen-grains not differing in size, are strongly 
opposed to this belief; on the other hand, the difference in 
length of the pistils in two of the plants, their sterility with 
their own pollen, and the difference in Jength and structure of 
the two sets of stamens in the same flower, and in the colour of 
their pollen, favour the belief. We know that when plants of 
any kind revert to a former condition, they are apt to be highly 
variable, and the two halves of the same organ sometimes differ 
much, as in the case of the above-described anther of the 
Lagerstreemia; we may therefore suspect that this species was 
once heterostyled, and that it still retains traces of its former 
state, together with a tendency to revert more completely to it. 
It deserves notice, as bearing on the nature of Lagerstrcemia, 
that in Lythrum hyssopifolia, which is a homostyled species, some 
of the shorter stamens vary in being either present or absent; 
and that these same stamens are altogether absent in L. thymi- 
folia. In another genus of the Lythracez, namely Cuphea, three 
species raised by me from seed certainly were homostyled ; 
nevertheless their stamens consisted of two sets, differing in 
length and in the colour and thickness of their filaments, but 
not in the size or colour of their pollen-grains; so that they 
thus far resembled the stamens of Lagerstreemia. I found that 
Cuphea purpurea was highly fertile with its own pollen when 
artificially aided, but sterile when insects were excluded.* 


* Mr. Spence informs me that phic: but he did not notice the 


In the 


in several species of the genus 
Mollia (Tiliaceze) which he col- 
lected in South America, the 
stamens of the five outer cohorts 
have purplish filaments and green 
pollen, whilst the stamens of the 
five inner cohorts have yellow 
pollen. He therefore suspected 
that these species might prove 
to be heterostyled and trimor- 


length of the pistils. 
allied Luhea the outer purplish 
stamens are destitute of anthers. 
I procured some specimens of 
Mollia lepidota and speciosa from 
Kew, but could not make out that 
their pistils differed in length 
in different plants; and in all 
those which I examined the 
stigma stood close beneath the 


Cuar. IV. OXALIS. 169 


OXALIS (GERANIACE). 


In 1863 Mr. Roland Trimen wrote to me from the 
Cape of Good Hope that he had there found species of 
Oxalis which presented three forms; and of these he 
enclosed drawings and dried specimens. Of one species 
he collected 43 flowers from distinct plants, and they 
consisted of 10 long-styled, 12 mid-styled, and 21 
short-styled. Of another species he collected 13 flowers, 
consisting of 3 long-styled, 7 mid-styled, and 3 short- 
styled. In 1866 Prof. Hildebrand provyed* by an ex- 
amination of the specimens in several herbaria that 20 
species are certainly heterostyled and trimorphic, and 
51 others almost certainly so: He also made some in- 
teresting observations on living plants belonging to 
one form alone; for at that time he did not possess 
the three forms of any living species. During the 
years 1864 to 1868 I occasionally experimented on 
Ozxalis speciosa, but until now have never found time 
to publish the results. In 1871 Hildebrand published 
an admirable papert in which he shows in the case of 
two species of Oxalis, that the sexual relations of the 
three forms are nearly the same as in Lythrum sali- 
earia. I will now give an abstract of his observa- 
tions, and afterwards of my own less complete ones. 
I may premise that in all the species seen by me, the 
stigmas of the five straight pistils of the long-styled 
form stand on a level with the anthers of the longest 
stamens in the two other forms. In the mid-styled 


uppermost anthers. The numerous * *Monatsber. der Akad. der 
stamens are graduated in length, Wiss. Berlin, 1866, pp. 352, 372. 
and the pollen-grains from the He gives drawings of the three 
longest and shortest ones did not _ forms at p. 42 of his ‘Geschlechter- 
present any marked difference in Vertheilung,’ &c., 1867. ; 
diameter. Therefore these species t ‘Bot. Zeitung, 1871, pp. 416 
do not appear to be heterostyled. and 432. 


170 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV. 


form, the stigmas pass out between the filaments of 
the longest stamens (as in the short-styled form of 
Linum); and they stand rather nearer to the upper 
anthers than to the lower ones. In the short-styled 


Long-styled. Mid-styled. Short-styled. 


OXALIS SPECIOSA (with the petals removed). 


SSS, stigmas. The dotted lines with arrows show which pollen must 
be carried to the stigmas for legitimate fertilisation. 

form, the stigmas also pass out between the filaments 
nearly on a level with the tips of the sepals. The 
anthers in this latter form and in the mid-styled rise 
to the same height as the corresponding stigmas in the 
other two forms. 

Oxalis Valdiviana.—This species, an inhabitant of 
the west coast of South America, bears yellow flowers. 


Hildebrand states that the stigmas of the three forms. 


do not differ in any marked manner, but that the pistil 
of the short-styled form alone is destitute of hairs. 
The diameters of the pollen-grains are as follows :— 


Divisions of the 
Micrometer. 


From the longest stamens of short-styled . . . . 8to09 
x mid-length —,, 99 Per merits hay 
- longest stamens of mid-styled . . . « 8 
a shortest oe “5 Sh Jounytel Mie 
mid-length stamens of long-styled . . . 7 
a shortest s a TES cae 


* 


Cuar. IV. OXALIS VALDIVIANA. 171 


Therefore the extreme difference in diameter is as 8°5 
to 6, or as 100 to 71. The results of Hildebrand’s ex- 
periments are given in the following table, drawn up 
in accordance with my usual plan. He fertilised each 
form with pollen from the two sets of anthers of the 
same flower, and likewise from flowers on distinct 
plants belonging to the same form; but the effects 
of these two closely allied kinds of fertilisation differ 
so little that I have not kept them distinct. 


TABLE 27. 
Oxalis Valdiviana (from Hildebrand). 


amber Number | Number 
A to) f of 
Nature of Union. Flowers coe Seeds per 
fertilised. | produced. | Capsule. 
Longestyled form, by pollen of longest | 
stamens of short-styled. Legitimate>| 28 28 16 I 
CT LUS cb eG SS iilec aes aC | 
| | 
Long-styled form, by pollen of longest 
stamens of mid-styled. Legitimate}| 21 21 12-0 
Tid 3 2) a ce ace || 
Long-styled form, by pollen of own and 
own-form mid-length stamens. Illegiti->| 40 2 5:5 
mate union Anh eee 
Long-styled form, by pollen of own and 
own-form shortest stamens.  Illegiti- 26 0 0 
SHRECRUMIOI TS Rec ose lls 
Long-styled form, by pollen of shortest 
stamens of short-styled. Illegitimate 16 1 1 
RMIT ook shor airs | ses 
Long-styled form, by pollen of shortest 
stamens of mid-styled. Illegitimate 9 0 0 
MSIMIOMETS er "us, | at MO NS ‘S : 


172 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV. 


TABLE 27—continued. 
Oxalis Valdiviana (from Hildebrand). 


SS 


Number | N usher N mane 
= - of co) 

Nature of Union. Flowers Capea Seeds per - 
fertilised. | produced. | Capsule. 


Short- styled form, by pollen of mid- length}| 
stamens of long - styled. Illegitimate 3 0 
WOO cls | oe. .he, yea ate ioe fe | 


Mid-styled form, by pollen of mid- length tas 38 38 11°3 F 
mers of long-styled, Legitimate union. | 
Mid-styled form, by pollen of mid-length | | 
stamens of short - styled. Legitimate 23 23 | 10°4 7 
union . | | | 
Mid-styled form, by pollen of own and)| | | ‘ 
own-form longest stamens. ee eT 52 0 0 q 
union . | | 
: — 
Mid-styled form, by pollen of own and)| | : 
own-form shortest stamens. Illegitimate ¢| 30 1 | 6 ; 
union. . | | { 
. 
Mid-styled ee = Piller i epee) | 
stamens of long-sty led. Illegitimate 16 0 0 4 
UMIONG {se Prey coays het | | 4 
| ! ‘a 
—_—— : 
“Mid- styled form, by pollen of longest sta-\! 4g | 9 2°5 
mens of short-styled. Llegitimate union : 
! 
| 
Short-styled form, by pollen of shortest sta- 18 18 11°0 
mens of long- -styled. Legitimate union. J| 
Short-styled form, by pollen of shortest sta- ’ . 
mens of mid-sty “led. Legitimate union } 10 10 11°3 4 
Short-styled form, by pollen of own and { 
own-form longest stamens. apie a1 0 0 
TUMIO MGs; Pls) Aire der~ . 
Short-styled form, by pollen of own and] | . 
own-form mid-length stamens, Illegiti- 22 ae hi 
mate union | 
Short-styled oa = pollen of longest sta- 4 0 | 0 
mens of mid-sty led. Illegitimate union 
| 


= 


Cuar. IV. OXALIS REGNELLL. 173 


We here have the remarkable result that every one 
of 138 legitimately fertilised flowers on the three forms 
yielded capsules, containing on an average 11°33 seeds. 
Whilst of the 255 illegitimately fertilised flowers, only 
6 yielded capsules, which contained 3°83 seeds on an 
average. Therefore the fertility of the six legitimate 
to that of the twelve illegitimate unions, as judged 
by the proportion of flowers that yielded capsules, is 
as 100 to 2, and as judged by the average number of 
seeds per capsule as 100 to 34. It may be added that 
some plants which were protected by nets did not 
spontaneously produce any fruit; nor did one which 
was left uncovered by itself and was visited by bees. 
On the other hand, scarcely a single flower on some 
uncovered plants of the three forms growing near 
together failed to produce fruit. 

Ozalis Regnelli—This species bears white flowers 
and inhabits Southern Brazil. Hildebrand says that 
the stigma of the long-styled form is somewhat larger 
than that of the mid-styled, and this than that of the 
short-styled. The pistil of the latter is clothed with a 
few hairs, whilst it is very hairy in the other two 
forms. The diameter of the pollen-grains from both 
sets of the longest stamens equals 9 divisions of the 
micrometer,—that from the mid-length stamens of the 
long-styled form between 8 and 9, and of the short- 
styled 8,—and that from the shortest stamens of both 
sets 7. So that the extreme difference in diameter is 
as 9 to 7 or as 100 to 78. The experiments made by 
Hildebrand, which are not so numerous as in the last 
case, are given in Table 28 in the same manner as 
before. 

The results are nearly the same as in the last case, 
but more striking; for 41 flowers belonging to the 
three forms fertilised legitimately all yielded capsules, 


be a a tlie 


3 


174 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV. 


TABLE 28. 
Oxalis Regnelli (from Hildebrand). 
eee or! Average ‘ 
; umber 0} 
cong "Ssh chgpees aware Capsules Seeds per 
| fertilised. | produced. | Capsule. 
Long-styled form, by pollen of longest sta-\) 6 — 6 | 10-1 
mens of short-styled. Legitimate union) | 
Long-styled form, by pollen of longest sta- 5 5 | 10°G 
mens of mid-styled. Legitimate union 
Long-styled form, by pollen of own mid-\/ 4 0 0 
length stamens. Illegitimate union S| 
Long-styled form, by pollen of own short-)_ 1 0 | 0 
est stamen. Illegitimate union. . 
Mid-styled form, by pollen of mid-length sta-) 9 9 10°4 
mens of short-styled. Legitimate union 
Mid-styled form, by pollen of mid- -length: sta- 10 10 10°1 | 
mens of long-styled. Legitimate union. | 
Mid-styled form, by pollen of own longest) 9 0 0 
stamens. Illegitimate union 
Mid-styled oa by pollen a: own sort) 9 0 0 
stamens. Ilegitimate union Si 
“Midistyled form, by pollen of longest sta-)! 1 | 0 0 
mens of short-styled. Illegitimate unions | 
| | 
Short-styled form, by pollen of shortest sta-)| 9 | 9 10°6 
mens of mid-styled. Legitimate union. 
Short-styled form, by pollen of shortest sta- 2 9 9°5 
mens of long-styled. Legitimate union. 
Short-styled form, by pollen of own mid- 12 | 0 0 
length stamens. Illegitimate union * 
Short-styled form, by pollen of own long-) 9 0 
est stamens. Illegitimate union ; | 0 
Short-styled form, by pollen of mid-length |: 
stamens of long-styled. Illegitimate 1 0 0 
anions, s Siels 7A oeeceecwss | 


Cuar. IV. OXALIS SPECIOSA. | 175 


containing on an average 10°31 seeds; whilst 39 
flowers fertilised illegitimately did not yield a single 
capsule or seed. Therefore the fertility of the six 
legitimate to that of the several illegitimate unions, 
as judged both by the proportion of flowers which 
yielded capsules and by the average number of con- 
tained seeds, is as 100 to 0. 

Oxzalis speciosa.—This species, which bears pink 
flowers, was introduced from the Cape of Good Hope. 
A sketch of the reproductive organs of the three 
forms (Fig. 11) has already been given. The stigma 
of the long-styled form (with the papille on its sur- 
face included) is twice as large as that of the short- 
styled, and that of the mid-styled intermediate in size. 
The pollen-grains from the stamens in the three forms 
are in their longer diameters as follows :— 


Divisions of the 


Micrometer. 
From the longest stamens of short-styled. . . 15 to 16 
os mid-length ,, + ule sew, ole tes ge 
» longest stamens of mid-styled . . . 16 
= shortest 39 os 11 to 12 
»  mid-length stamens of long-styled. . 14 
= shortest == = Sees 12 


Therefore the extreme difference in diameter is as 
16 to 11, or as 100 to 69; but as the measurements 
were taken at different times, they are probably only 
approximately accurate. The results of my experiments 
in fertilising the three forms are given in the following 
table. 


*176 HETEROSTYLED TRIMORPHIC PLANTS. Cuapr. IV 


TABLE 29, 


Oxalis speciosa. 


' 
| Number | Number | Average 
Ce of Number of 
Flowers | Capsules | Seeds per 
| fertilised. | erste. | Capsule. 


Nature of Union 


union . . . . . . 


Long-styled form, by pollen of longest 
stamens of short -styled. Drasrati 57°4 
union. . - 
Pepe es form, by pollen of lonpent)| aa 
stamens of * mid - styled. Legitimate 3 59°0 
union . cs an : 
Long-styled form, by es of own-form), 9 ea el 9 42°5 
mid-length stamens. Illegitimate union 
onetoed form, by pollen of own-form feet 0 0 : 
shortest stamens. Illegitimate union ite. poe 
Long-styled form, by eye of shortest oF 
stamens of mid- “styled, Illegitimate >| 0 0 
union. 
ene form, by pollen of mid-length)}| 
stamens of short-styled. ae 12 5 30°0 
union . ome 
Mid-styled form, by pollen of mid- “ape 
stamens of long - styled. Legitimate 3 3 63° 6 
DMION Si eaten > eS) | 
Mid-styled form, by pollen of mid- length). | ‘ 
_ Stamens of short - elneatl Legitimate} 4 a 56°3 
union . ; | 
Mid-styled form, by mixed puter from || | 
both own-form longest and shortest} 9 | 2 19 
stamens. Illegitimate union “ht 
2 aT 
stamens of short-styled. eal ite 1 ae ae 8 


Mid-styled form, by pollen of a 
| 


— ae. 


Ouar. 1V. OXALIS SPECIOSA. Wa 


TABLE 29—continued. 


Oxalis speciosa. 


Number | Number | Average 


F of of |Number of 
Nature of Union. Flowers | Capsules | Seeds per 
fertilised. | produced. | Capsule. 
Short-styled form, by pollen of shortest )| | 
stamens of mid - styled. gue 3 2 67 
union. .  . . | 
" Short-styled form, by pollen of shortest | 
stamens of long-styled. Satie 3 3 54°3 
union. . aey* 
Short-styled form, by pollen af own form) 5 1 8 
longest stamens. Illegitimate union J 
Short-styled form, by pollen of own-form 3 0 0 
mid-length stamens. Illegitimate union 
Short-styled form, by both pollens mixed | 
together, of own-torm longest and mid- 13 mu 0 
length stamens. Illegitimate union | 
Short-styled form, by pollen of longest 
stamens of mid-styled. Illegitimate 7 0 0 
HIG eis) sell e 
Short-styled form, by pollen of mid-length Al 
stamens of long - are peste 1 54 
union . - 


We here see that thirty-six flowers on the three 
forms legitimately fertilised yielded 30 capsules, these 
containing on an average 58°36 seeds. Ninety-five 
flowers illegitimately fertilised yielded 12 capsules, 
containing on an average 28°58 seeds. Therefore the 
fertility of the six legitimate to that of the twelve 
illegitimate unions, as judged by the proportion of 
flowers which yielded capsules, is as 100 to 15, and 
judged by the average number of seeds per capsule as 
100 to 49. This plant, in comparison with the two 
South American species previously described, produces 


“178  HETEROSTYLED TRIMORPHIC PLANTS. Cuar IV. 


many more seeds, and the illegitimately fertilised 
flowers are not quite so sterile. 

Oxalis rosea.—Hildebrand possessed in a living state 
only the long-styled form of this trimorphic Chilian 
species.* The pollen-grains from the two sets of 
anthers differ in diameter as 9 to 7°5, or as 100 to 83. 
He has further shown that there is an analogous 
difference between the grains from the two sets of 
anthers of the same flower in five other species of Oxalis, 
besides those already described. The present species 
differs remarkably from the long-styled form of the 
three species previously experimented on, in a much 
larger proportion of the flowers setting capsules when 
fertilised with their own-form pollen. Hildebrand fer- 
tilised 60 flowers with pollen from the mid-length 
stamens (of either the same or another flower), and 
they yielded no less than 55 capsules, or 92 per cent. 
These capsules contained on an average 5°62 seeds; 
but we have no means of judging how near an approach 
this average makes to that from flowers legitimately 
fertilised. He also fertilised 45 flowers with pollen 
from the shortest stamens, and these yielded only 17 
capsules, or 31 per cent., containing on an average 
only 2°65 seeds. We thus see that about thrice as 
many flowers, when fertilised with pollen from the 
mid-length stamens, produced capsules, and these 
contained twice as many seeds, as did the flowers 
fertilised with pollen from the shortest stamens. 
It thus appears (and we find some evidence of 
the same fact with O. speciosa), that the same rule 
holds good with Oxalis as with Lythrum salicaria ; 
namely, that in any two unions, the greater the in- 
equality in length between the pistils and stamens, or, 


* ‘Monatsber, der Akad. der Wiss. Berlin,’ 1866, p. 372. 


Cuap. IV. OXALIS, OTHER SPECIES OF. 179 


which is the same thing, the greater the distance of 
the stigma from the anthers, the pollen of which is 
used for fertilisation, the less fertile is the union,— 
whether judged by the proportion of flowers which 
set capsules, or by the average number of seeds per 
capsule. The rule cannot be explained in this case 
any more than in that of Lythrum, by supposing 
that wherever there is greater liability to self-fertilisa- 
tion, this is checked by the union being rendered more 
sterile; for exactly the reverse occurs, the liability to 
self-fertilisation being greatest in the unions between 
the pistils and stamens which approach each other the 
nearest, and these are the more fertile. I may add 
that I also possessed some long-styled plants of this 
species: one was covered by a net, and it set sponta- 
neously a few capsules, though extremely few com- 
pared with those produced by a plant growing by 
itself, but exposed to the visits of bees. 

With most of the species of Oxalis the short-styled 
form seems to be the most sterile of the three forms, 
when these are illegitimately fertilised ; and I will add 
two other cases to those already given. I fertilised 
29 short-styled flowers of O. compressa with pollen from 
their own two sets of stamens (the pollen-grains of 
which differ in diameter as 100 and 83), and not one 
produced a capsule. I formerly cultivated during 
several years the short-styled form of a species pur- 
chased under the name of 0. Bowii (but I have some 
doubts whether it was rightly named), and fertilised 
many flowers with their own two kinds of pollen, 
which differ in diameter in the usual manner, but 
never got a single seed. On the other hand, Hilde- 
brand says that the short-styled form of O. Deppei, 
growing by itself, yields plenty of seed ; but it is not 
positively known that this species is heterostyled ; and 


180 HETEROSTYLED TRIMORPHIC PLANTS. Caap. LV. 


the pollen-grains from the two sets of anthers do not 
differ in diameter. 

Some facts communicated to me by Fritz Miller 
afford excellent evidence of the utter sterility of one 
of the forms of certain trimorphic species of Oxalis, 
when growing isolated. He has seen in St. Catharina, 
in Brazil, a large field of young sugar-cane, many 
acres in extent, covered with the red blossoms of one 
form alone, and these did not produce a single seed. 
His own Jand is covered with the short-styled form of 
a white-flowered trimorphic species, and this is equally 
sterile ; but when the three forms were planted near 
together in his garden they seeded freely. With two 
other trimorphic species he finds that isolated plants 
are always sterile. 

Fritz Miller formerly believed that a species of 
Oxalis, which is so abundant in St. Catharina that it 
borders the roads for miles, was dimorphic instead of 
trimorphic. Although the pistils and stamens vary 
greatly in length, as was evident in some specimens 
sent to me, yet the plants can be divided into two 
sets, according to the lengths of these organs. A 
large proportion of the anthers are of a white colour 
and quite destitute of pollen; others which are pale 
yellow contain many bad with some good grains; and 
others again which are bright yellow have apparently 
sound pollen; but he has never succeeded in finding 
any fruit on this species. The stamens in some of 
the flowers are partially converted into petals. Fritz 
Miller after reading my description, hereafter to be 
siven, of the illegitimate offspring of various hetero- 
styled species, suspects that these plants of Oxalis 
may be the variable and sterile offspring of a single 
form of some trimorphic species, perhaps accidentally 
introduced into the district, which has since been 


| 
4 
| 
F 
’ 
| 
7 
q 


Cuar. IV. OXALIS, HOMOSTYLED SPECIES. 181 


propagated asexually. It is probable that this kind 
of propagation would be much aided by there being 
no expenditure in the production of seed. 

Ozxalis (Biophytum) sensitiva—This plant is ranked 
by many botanists as a distinct genus. Mr. Thwaites 
sent me a number of flowers preserved in spirits from 
Ceylon, and they are clearly trimorphic. The style 
of the long-styled form is clothed with many scattered 
hairs, both simple and glandular; such hairs are much 
fewer on the style of the mid-styled, and quite ab- 
sent from that of the short-styled form; so that this 
plant resembles in this respect O. Valdiviana and 


_Regnelli. Calling the length of the two lobes of 


the stigma of the long-styled form 100, that of 
the mid-styled is 141, and that of the short-styled 
164. In all other cases, in which the stigma in this 
genus differs in size in the three forms, the differ- 
ence is of a reversed nature, the stigma of the long- 
styled being the largest, and that of the short-styled 
the smallest. The diameter of the pollen-grains from 
the longest stamens being represented by 100, those 
from the mid-length stamens are 91, and those from 
the shortest stamens 84 in diameter. This plant is 
remarkable, as we shall see in the last chapter of 
this volume, by producing long-styled, mid-styled, 
and short-styled cleistogamic flowers. 


Homostyled Species of Oxalis——Although the majority 
of the species in the large genus Oxalis seem to be 
trimorphic, some are homostyled, that is, exist under 
a single form; for instance the common O. aceto- 
sella, and according to Hildebrand two other widely 
distributed European species, O. stricta and corniculata. 
Fritz Miller also informs me that a similarly consti- 
tuted species is found in St. Catharina, and that it is 


182 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV. 


quite fertile with its own pollen when insects are ex- 
cluded. The stigmas of O. stricta and of another homo- 
styled species, viz. O. tropxoloides, commonly stand on 
a level with the upper anthers, and both these species 
are likewise quite fertile when insects are excluded. 
With respect to O. acetosella, Hildebrand says that in 
all the many specimens examined by him the pistil 
exceeded the longer stamens in length. I procured 
108 flowers from the same number of plants growing in 
three distant parts of England; of these 86 had their 
stigmas projecting considerably above, whilst 22 had 
them nearly on a level with the upper anthers. In 
one lot of 17 flowers from the same wood, the stigmas in 
every flower projected fully as much above the upper 
anthers as these stood above the lower anthers. So 
that these plants might fairly be compared with the 
long-styled form of a heterostyled species; and I at 
first thought that O. acetosella was trimorphic. But 
the case is one merely of great variability. The 
pollen-grains from the two sets of anthers, as observed 
by Hildebrand and myself, do not differ in diameter. 
I fertilised twelve flowers on several plants with pol- 
len from a distinct plant, choosing those with pistils 
ot a different length; and 10 of these (i.e. 83 per cent.) 
produced capsules, which contained on an average 7:9 
seeds. Fourteen flowers were fertilised with their own 
pollen, and 11 of these (i.e. 79 per cent.) yielded cap- 
sules, containing a larger average of seed, namely 9:2. 
These plants, therefore, in function show not the 
least sign of being heterostyled. I may add that 18 
flowers protected by a net were left to fertilise them- 
selves, and only 10 of these (i.e. 55 per cent.) yielded 
capsules, which contained on an average only 6:3 seeds. 
So that the access of insects, or artificial aid in placing 
pollen on the stigma, increases the fertility of the 


Cuar. IV. PONTEDERIA. 183 


flowers; and I found that this applied especially to 
those haying shorter pistils. It should be remem- 
bered that the flowers hang downwards, so that those 
with short pistils would be the least likely to receive 
their own pollen, unless they were aided in some 
manner. 

Finally, as Hildebrand has remarked, there is no 
evidence that any of the heterostyled species of Oxalis 
are tending towards a dicecious condition, as Zuccarini 
and Lindley inferred from the differences in the re- 
productive organs of the three forms, the meaning of 
which they did not understand. 


PONTEDERIA [SsP.?] (PONTEDERIACEZ.) 


Fritz Miller found this aquatic plant, which is al- 
lied to the Liliaceze, growing in the greatest profusion 
on the banks of a river in Southern Brazil.* But only 
two forms were found, the flowers of which include 
three long and three short stamens. The pistil of the 
long-styled form, in two dried flowers which were sent 
me, was in length as 100 to 32, and its stigma as 100 
to 80, compared with the same organs in the short- 
styled form. The long-styled stigma projects conside- 
rably above the upper anthers of the same flower, and 
stands on a level with the upper ones of the short-stylied 
form. In the latter the stigma is seated beneath both its 
own sets of anthers, and is on a level with the anthers 
of the shorter stamens in the long-styled form. The 
anthers of the longer stamens of the short-styled form 
are to those of the shorter stamens of the long-styled 
form as 100 to 88 in length. The pollen-grains distended 


*«“Ueber den Trimorphismus Zeitschrift? &c., Band 6, 1871, 
der Pontederien”; ‘Jenaische p. 74. 


9 


184. HETEROSTYLED TRIMORPHIC PLANTS. Cwap. IV. 


with water from the longer stamens of the short-styled 
form are to those from the shorter stamens of the same 
form as 100 to 87 in diameter, as deduced from ten 
measurements of each kind. We thus see that the 
organs in these two forms differ from one another 
and are arranged in an analogous manner, as in the 
long and short-styled forms of the trimorphie species 
of Lythrum and Oxalis. Moreover, the longer stamens 
of the long-styled form of Pontederia, and the shorter 
ones of the short-styled form are placed in a proper 
position for fertilising the stigma of a mid-styled form. 
But Fritz Miller, although he examined a vast number 
of plants, could never find one belonging to the mid- 
styled form. The older flowers of the long-styled 
and short-styled plants had set plenty of apparently 
good fruit; and this might have been expected, as 
they could legitimately fertilise one another. AlI- 
though he could not find the mid-styled form of 
this species, he possessed plants of another species 
crowing in his garden, and all these were mid-styled ; 
and in this case the pollen-grains from the anthers of 
the longer stamens were to those from the shorter sta- 
mens of the same flower as 100 to 86 in diameter, as 
deduced from ten measurements of each kind. These 
mid-styled plants growing by themselves never pro- 
duced a single fruit. 

Considering these several facts, there can hardly be 
a doubt that both these species of Pontederia are 
heterostyled and trimorphic. This case is an interest- 
ing one, for no other Monocotyledonous plant is known 
to be heterostyled. Moreover, the flowers are irregular, 
and all other heterostyled plants have almost sym- 
metrical flowers. The two forms differ somewhat in 
the colour of their corollas, that of the short-styled 
being of a darker blue, whilst that of the long-styled 


oe ee er oe 


Crap. IV. PONTEDERLIA. 185 


tends towards violet, and no other such case is known. 
Lastly, the three longer stamens alternate with the 
three shorter ones, whereas in Lythrum and Oxalis 
the long and short stamens belong to distinct whorls. 
With respect to the absence of the mid-styled form in 
the case of the Pontederia which grows wild in Southern 
Brazil, this would probably follow if only two forms 
had been originally introduced there ; for, as we shall 
hereafter see from the observations of Hildebrand, 
Fritz Miller and myself, when one form of Oxalis is 
fertilised exclusively by either of the other two forms, 
the offsprig generally belong to the two parent- 
forms. 

Fritz Miller has recently discovered, as he informs 
me, a third species of Pontederia, with all three forms 
growing together in pools in the interior of 8. Brazil ; 

so that no shadow of doubt can any longer remain 
- about this genus including trimorphie species. He 
sent me dried flowers of all three forms. In the long- 
styled form the stigma stands a little above the tips of 
the petals, and on a level with the anthers of the 
longest stamens in the other two forms. The pistil is 
in length to that of the mid-styled as 100 to 56, and 
to that of the short-styled as 100 to 16. Its summit is 
rectangularly bent upwards, and the stigma is rather 
broader than that of the mid-styled, and broader in 
about the ratio of 7 to 4 than that of the short-styled. 
In the mid-styled form, the stigma is placed rather 
above the middle of the corolla, and nearly on a level 
with the mid-length stamens in the other two forms; 
its summit is a little bent upwards. In the short- 
styled form the pistil is, as we have seen, very short, 
and differs from that in the other two forms in being 
straight. It stands rather beneath the level of the 
anthers of the shortest stamens in the long-styled and 


186 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV. 


mid-styled forms. The three anthers of each set of 
stamens, more especially those of the shortest stamens, 
are placed one beneath the other, and the ends of the 
filaments are bowed a little upwards, so that the pollen 
from all the anthers would be effectively brushed off 
by the proboscis of a visiting insect. ‘The relative 
diameters of the pollen-grains, after having been long 
soaked in water, are given in the following list, as 
measured by my son Francis. 


Divisions of the 


Micrometer. 
Long-styled form, from the mid-length stamens . . . 13°2 
(Average of 20 measurements.) 

He aS from the shortest stamens . . . . 9°0 
(10 measurements.) 

Mid-styled form, from the longest stamens . . . . 16°4 
(15 measurements.) 

As ss from the shortest stamens. . . . Q97°1 
(20 measurements.) 

Short-styled form, from the longest stamens . . . . 14°6 
(20 measurements.) 

os rs from the mid-length stamens . . . 12°3 


(20 measurements.) 


We have here the usual rule of the grains from the 
longer stamens, the tubes of which have to penetrate 
the longer pistil, being larger than those from the 
stamens of less length. The extreme difference in 
diameter between the grains from the longest stamens 
of the mid-styled form, and from the shortest stamens 
of the long-styled, is as 16°4 to 9:0, or as 100 to 55; 
and this is the greatest difference observed by me in 
any heterostyled plant. It is a singular fact that the 
grains from the corresponding longest stamens in the 
two forms differ considerably in diameter; as do those 
in a lesser degree from the corresponding mid-length 
stamens in the two forms; whilst those from the cor- 
responding shortest stamens in the long- and mid- 
styled forms are almost exactly equal. ‘Their in- 
equality in the two first cases depends on the grains 


Cuar. IV. PONTEDERIA. 187 


in both sets of anthers in the short-styled form being 
smaller than those from the corresponding anthers in 
the other two forms; and here we have a case parallel 
with that of the mid-styled form of Lythrum salicaria. 
In this latter plant the pollen-grains of the mid-styled 
forms are of smaller size and have less fertilising power 
than the corresponding ones in the other two forms ; 
whilst the ovarium, however fertilised, yields a greater 
number of seeds; so that the mid-styled form is alto- 
gether more feminine in nature than the other two 
forms. In the case of Pontederia, the ovarium in- 
cludes only a single ovule, and what the meaning of 
the difference in size between the pollen-grains from 
the corresponding sets of anthers may be, I will not 
pretend to conjecture. 

The clear evidence that the species just described is 
heterostyled and trimorphic is the more valuable as 
there is some doubt with respect to P. cordata, an in- 
habitant of the United States. Mr. Leggett suspects * 
that it is either dimorphic or trimorphic, for the 
pollen-grains of the longer stamens are “more than 
twice the diameter or than eight times the mass of 
the grains of the shorter stamens. Though minute, 
these smaller grains seem as perfect as the larger 
ones.” On the other hand, he says that in all the 
mature flowers, “the style was as long at least as 
the longer stamens;” “whilst in the young flowers 


* it was intermediate in length between the two sets of 


stamens ;” and if this be so, the species can hardly be 
heterostyled. 


* ‘Bull. of the Torrey Botanical Club,’ 1875, vol. vi. p. 62. 


188 ILLEGITIMATE OFFSPRING OF Cuap. Y. 


CHAPTER V. 


ILLEGITIMATE OFrrsPRING OF HETEROSTYLED PLANTS. 


Illegitimate offspring from all three forms of Lythrum salicaria—Their 
dwarfed stature and sterility, some utterly barren, some fertile— 
Oxalis, transmission of form to the legitimate and illegitimate 
seedlings—Primula Sinensis, illegitimate offspring in some degree 
dwarfed and infertile—Equal-styled varieties of P. Sinensis, auri- 
cula, farinosa, and elatior—P. vulgaris, red-flowered variety, illegi- 
timate seedlings sterile—P. veris, illegitimate plants raised during 
several successive generations, their dwarfed stature and sterility— 
Equal-styled varieties of P. veris—Transmission of form by Pul- 
monaria and Polygonum—Concluding remarks—Close parallelism 
between illegitimate fertilisation and hybridism. 

WE have hitherto treated of the fertility of the flowers 

of heterostyled plants, when legitimately and illegiti- 

mately fertilised. The present chapter will be devoted 
to the character of their offspring or seedlings. Those 
raised from legitimately fertilised seeds will be here 
called legitimate seedlings or plants, and those from 
illegitimately fertilised seeds, illegitimate seedlings or 
plants. They differ chiefly in their degree of fertility, 
and in their powers of growth or vigour. I will begin 
with trimorphic plants, and I must remind the reader 
that each of the three forms can be fertilised in six 
different ways; so that all three together can be ferti- 
lised in eighteen different ways. or instance, a 
long-styled form can be fertilised legitimately by the 
longest stamens of the mid-styled and _ short-styled 
forms, and illegitimately by its own-form mid-length 
and shortest stamens, also by the mid-length stamens 
of the mid-styled and by the shortest stamens of the 
short-styled form; so that the long-styled can be ferti- 


Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 189 


lised legitimately in two ways and illegitimately in 
four ways. The same holds good with respect to the 
mid-styled and short-styled forms. Therefore with 
trimorphie species six of the eighteen unions yield 
legitimate offspring, and twelve yield illegitimate 
offspring. 

I will give the results of my experiments in detail, 
partly because the observations are extremely trouble- 
some, and will not probably soon be repeated—thus, I 
was compelled to count under the microscope above 
20,000 seeds of Lythrum salicaria—but chiefly because 
light is thus indirectly thrown on the important sub- 
ject of hybridism. 


LYTHRUM SALICARIA. 


Of the twelve illegitimate unions two were com- 
pletely barren, so that no seeds were obtained, and of 
course no seedlings could be raised. Seedlings were, 
however raised from seven of the ten remaining il- 
legitimate unions. Such illegitimate seedlings when 
in flower were generally allowed to be freely and 
legitimately fertilised, through the agency of bees, by 
other illegitimate plants belonging to the two other 
forms growing close by. This is the fairest plan, and 
was usually followed; but in several cases (which 
will always be stated) Ulegitimate plants were ferti- 
lised with pollen taken from legitimate plants be- 
Jonging to the other two forms; and this,as might 
have been expected, increased their fertility. Lythrum 
salicaria is much affected in its fertility by the nature 
of the season; and to avoid error from this source, 
as far as possible, my observations were continued 
during several years. Some few experiments were 
tried in 1863. The summer of 1864 was too hot and 


190 ILLEGITIMATE OFFSPRING OF Cuar. V. 


dry, and, though the plants were copiously watered, 
some few apparently suffered in their fertility, whilst 
others were not in the least affected. The years 
1865 and, especially, 1866, were highly favourable. 
Only a few observations were made during 1867. 
The results are arranged in classes according to the 
parentage of the plants. In each case the average 
number of seeds per capsule is given, generally taken 
from ten capsules, which, according to my experience, 
is a nearly sufficient number. The maximum num- 
ber of seeds in any one capsule is also given; and 
this is a useful point of comparison with the nor- 
mal standard—that is, with the number of seeds 
produced by legitimate plants legitimately ferti- 
lised. I will give likewise in each case the minimum 
number. When the maximum and minimum differ 
ereatly, if no remark is made on the subject, it may 
be understood that the extremes are so closely con- 
nected by intermediate figures that the average is a 
fair one. Large capsules were always selected for 
counting, in order to avoid over-estimating the infer- 
tility of the several illegitimate plants. 

In order to judge of the degree of inferiority in 
fertility of the several illegitimate plants, the follow- 
ing statement of the average and of the maximum 


number of seeds produced by ordinary or legitimate 


plants, when legitimately fertilised, some artificially 
and some naturally, will serve as a standard of com- 
parison, and may in each case be referred to. But I 
give under each experiment the percentage of seeds 
produced by the illegitimate plants, in comparison 
with the standard legitimate number of the same 
form. For instance, ten capsules from the illegitimate 
long-styled plant (No. 10), which was legitimately 


and naturally fertilised by other illegitimate plants, — 


—S SS ee a ee 


Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 191 


contained on an average 44°2 seeds; whereas the 
capsules on legitimate long-styled plants, legitimately 
and naturally fertilised by other legitimate plants, 
contained on an average 93 seeds. ‘Therefore this 
illegitimate plant yielded only 47 per cent. of the 
full and normal complement of seeds. 


Standard Number of Seeds produced by Legitimate Plants 
of the three Forms, when legitimately fertilised. 


Long-styled form: average number of seeds in each 
capsule, 93 ; maximum number observed out of twenty- 
three capsules, 159. 

Mid-styled form: average number of seeds, 150; 
maximum number observed out of thirty-one capsules, 
151. 

Short-styled form: average number of seeds, 85°5 ; 
but we may, for the sake of brevity, say 83; maximum 
number observed out of twenty-five capsules, 112. 


Cuasses I. and II. Illegitimate Planis raised from 
Long-styled Parents fertilised with pollen from the 
mid-length or the shortest stamens of other plants of 
the same form. 


From this union I raised at different times three 
lots of illegitimate seedlings, amounting altogether to 
56 plants. I must premise that, from not foreseeing 
the result, I did not keep a memorandum whether the 
eight plants of the first lot were the product of the 
mid-length or shortest stamens of the same form ; but 
I haye good reason to believe that they were the pro- 
duct of the latter. These eight plants were much more 
dwarfed, and much more sterile than those in the other 
two lots. The latter were raised from a long-styled 


192 ILLEGITIMATE OFFSPRING OF Cuap. V. 


plant growing quite isolated, and fertilised by the 
agency of bees with its own pollen; and it is almost 
certain, from the relative position of the organs of 
fructification, that the stigma under these circum- 
stances would receive pollen from the mid-length 
stamens. 

All the fifty-six plants in these three lots proved long- 
styled ; now, if the parent-plants had been legitimately 
fertilised by pollen from the longest stamens of the 
mid-styled and short-styled forms, only about one- 
third of the seedlings would have been long-styled, 
the other two-thirds being mid-styled and short-styled. 


- In some other trimorphic and dimorphic genera we 


shall find the same curious fact, namely, that the long- 
styled form, fertilised illegitimately by its own-form 
pollen, produces almost exclusively long-styled seed- 
lings.* 

The eight plants of the first lot were of low stature: 
three which I measured attained, when fully grown, the 
heights of only 28, 29, and 47 inches; whilst legitimate 
plants growing close by were double this height, one 
being 77 inches. They all betrayed in their general 
appearance a weak constitution ; they flowered rather 
later in the season, and at a later age than ordinary 
plants. Some did not flower every year ; and one plant, 
behaving in an unprecedented manner, did not flower 
until three years old. In the two other lots none of 
the plants grew quite to their full and proper height, 
as could at once be seen by comparing them with the 
adjoining rows of legitimate plants. In several plants 
in all three lots, many of the anthers were either 
shrivelled or contained brown and tough, or pulpy 


* Hildebrand first called atten- of Primula Sinensis ; but his re- 
tion (‘ Bot. Zeitung, Jan. 1, 1864, sults were not nearly so uniform 
p. 5) to this fact in the case as mine. 


Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 193 


matter, without any good pollen-grains, and they never 
shed their contents ; they were in the state designated 
by Gartner * as contabescent, which term I will for the 
future use. In one flower all the anthers were conta- 
bescent excepting two which appeared to the naked 
eye sound ; but under the microscope about two-thirds 
of the pollen-grains were seen to be small and shrivelled. 
In another plant, in which all the anthers appeared 
sound, many of the pollen-grains were shrivelled and 
of unequal sizes. I counted the seeds produced by 
seven plants (1 to 7) in the first lot of eight plants, 
probably the product of parents fertilised by their 
own-form shortest stamens, and the seeds produced by 
three plants in the other two lots, almost certainly the 
product of parents fertilised by their own-form mid- 
Jength stamens. 


Plant 1. This leng-styled plant was allowed during 1863 to 
be freely and legitimately fertilised by an adjoining illegitimate 
mid-styled plant, but it did not yield a single seed-capsule. It 
was then removed and planted in a remote place close to a 
brother long-styled plant No. 2, so that it must have been freely 
though illegitimately fertilised; under these circumstances it 
did not yield during 1864 and 1865 a single capsule. I should 
here state that a legitimate or ordinary long-styled plant, when 
growing isolated, and freely though illegitimately fertilised by 
insects with its own pollen, yielded an immense number of 
capsules, which contained on an average 21°5 seeds. 

Plant 2. This long-styled plant, after flowering during 1863 
close to an illegitimate mid-styled plant, produced less than 
twenty capsules, which contained on an average between four 
and five seeds. When subsequently growing in company with 
No. 1, by which it will have been illegitimately fertilised, it 
yielded in 1866 not a single capsule, but in 1865 it yielded 
twenty-two capsules: the best of these, fifteen in number, were 
examined; eight contained no seed, and the remaining seven 
contained on an average only three seeds, and these seeds were 


* «Beitrage zur Kenntniss der Befruchtung, 1844, p. 116. 


194 ILLEGITIMATE OFFSPRING OF Cuar. V. 


so small and shrivelled that I doubt whether they would have 
germinated. 

Plants 3 and 4. These two long-styled plants, after being 
freely and legitimately fertilised during 1863 by the same iile- 
gitimate mid-styled plant as in the last case, were as miserably 
sterile as No. 2. 

Plant 5. This long-styled plant, after flowering in 1863 close 
to an illegitimate mid-styled plant, yielded only four capsules, 
which altogether included only five seeds. During 1864, 1865, 
and 1866, it was surrounded either by illegitimate or legitimate 
plants of the other two forms; but it did not yield a single 
capsule. It was a superfluous experiment, but I likewise arti- 
ficially fertilised in a legitimate manner twelve flowers; but not 
one of these produced a capsule; so that this plant was almost 
absolutely barren. 

Plant 6. This long-styled plant, after flowering during the 
favourable year of 1866, surrounded by illegitimate plants of 
the other two forms, did not produce a single capsule. 

Piant 7. This long-styled plant was the most fertile of the 
eight plants of the first lot. During 1865 it was surrounded by 
illegitimate plants of various parentage, many of which were 
highly fertile, and must thus have been legitimately fertilised. 
It produced a good many capsules, ten of which yielded an 
average of 86°1 seeds, with a maximum of 47 and a minimum 
of 22; so that this plant produced 39 per cent. of the full 
number of seeds. During 1864 it was surrounded by legitimate 
and illegitimate plants of the other two forms; and nine 
capsules (one poor one being rejected) yielded an average of 
41:9 seeds, with a maximum of 56 and a minimum of 28; so 
that, under these favourable circumstances, this plant, the most 


fertile of the first lot, did not yield, when legitimately fertilised, 


quite 45 per cent. of the full complement of seeds. 


In the second lot of plants in the present class, 
descended from the long-styled form, almost certainly 
fertilised with pollen from its own mid-length stamens, 
the plants, as already stated, were not nearly so dwarfed 
or so sterile as in the first lot. All produced plenty 
of capsules. J counted the number of seeds in only 
three plants, viz. Nos. 8, 9, and 10. 


Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 195 


Plant 8. This plant was allowed to be freely fertilised in 1864 
by legitimate and illegitimate plants of the other two forms, 
and ten capsules yielded on an average 41°1 seeds, with a 
maximum of 73 and a minimum of 11. Hence this plant pro- 
duced only 44 per cent. of the full complement of seeds. 

Plant 9. This long-styled plant was allowed in 1865 to be 
freely fertilised by illegitimate plants of the other two forms, 
most of which were moderately fertile. Fifteen capsules yielded 
on an average 57°1 seeds, with a maximum of 86 and a minimum 
of 23. Hence the plant yielded 61 per cent. of the full comple- 
ment of seeds. 

Plant 10 This long-styled plant was freely fertilised at the 
same time and in the same manner as the last. Ten capsules 
yielded an average of 44°2 seeds, with a maximum of 69 anda 
minimum of 25; hence this plant yielded 47 per cent. of the 
full complement of seeds. 


The nineteen long-styled plants of the third lot, of 
the same parentage as the last lot, were treated dif- 
ferently ; for they flowered during 1867 by themselves 
so that they must have been illegitimately fertilised 
by one another. It has already been stated that a 
legitimate long-styled plant, growing by itself and 
visited by insects, yielded an average of 21-5 seeds 
per capsule, with a maximum of 35; but, to judge 
fairly of its fertility, it ought to have been observed 
during successive seasons. We may also infer from 
analogy that, if several legitimate long-styled plants 
were to fertilise one another, the average number of 
seeds would be increased; but how much increased 
I do not know; hence I have no perfectly fair standard 
of comparison by which to judge of the fertility of the 
three following plants of the present lot, the seeds of 
which I counted. 


Plant 11. This long-styled plant produced a large crop of 
capsules, and in this respect was one of the most fertile of 
the whole lot of nineteen plants. But the average from ten 


196 ILLEGITIMATE OFFSPRING OF Cuar. VY. 


capsules was. only 35°9 seeds, with a maximum of 60 anda 
minimum of 8. 

Plant 12. This long-styled plant produced very few capsules; 
and ten yielded an average of only 15:4 seeds, with a maximum 
of 50 and a minimum of 4. 

Plant 13. This plant offers an anomalous case; it flowered 
profusely, yet produced very few capsules; but these con- 
tained numerous seeds. Ten capsules yielded an average of 
71:9 seeds, with a maximum of 95 and a minimum of 29. Con- 
sidering that this plant was illegitimate and illegitimately fer- 
tilised by its brother long-styled seedlings, the average and the 
maximum are so remarkably high that I cannot at all under- 
stand the case. We should remember that the average for a 
legitimate plant legitimately fertilised is 93 seeds. 


Cuass IIL. Illegitimate Plants raised from a Short- 
styled Parent fertilised with pollen from own-form 
mid-length stamen. 


I raised from this union nine plants, of which eight 
were short-styled and one long-styled; so that there 
seems to be a strong tendency in this form to repro- 
duce, when self-fertilised, the parent-form; but the 
tendency is not so strong as with the long-styled. 
These nine plants never attained the full height of 
legitimate plants growing close to them. The anthers 
were contabescent in many of the flowers on several 
plants. 


Plant 14. This short-styled plant was allowed during 1865 to 
be freely and legitimately fertilised by illegitimate plants de- 
scended from self-fertilised mid-, long- and short-styled plants. 
Fifteen capsules yielded an average of 28°3 seeds, with a 
maximum of 51 and a minimum of 11; hence this plant 
produced only 83 per cent. of the proper number of seeds. The 
seeds themselves were small and irregular in shape. Although 
so sterile on the female side, none of the anthers were conta- 
bescent. 

Plant 15, This short-styled plant, treated like the last during 


; 
; 
} 


—_ 


Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 197 


the same year, yielded an average, from fifteen capsules, of 27 
seeds, with a maximum of 49 anda minimum of 7. But two 
poor capsules may be rejected, and then the average rises to 
32:6, with the same maximum of 49 and a minimum of 20; so 
that this plant attained 38 per cent. of the normal standard of 
fertility, and was rather more fertile than the last, yet many of 
the anthers were contabescent. 

Piant 16. This short-styled plant, treated like the two last, 
yielded from ten capsules an average of 77°8 seeds, with a 
maximum of 97 and a minimum of 60; so that this plant 
produced 94 per cent. of the full number of seeds. 

Plant 17. This, the one long-styled plant of the same parent- 
age as the last three plants, when freely and legitimately ferti- 
lised in the same manner as the last, yielded an average from 
ten capsules of 76°3 rather poor seeds, with a maximum of 85 
and a minimum of 57. Hence this plant produced 82 per cent. 
of the proper number of seeds. Twelve flowers enclosed in a 
net were artificially and legitimately fertilised with pollen from 
a legitimate short-styled plant; and nine capsules yielded an 
average of 82°5 seeds, with a maximum of 98 and a minimum 
of 51; so that its fertility was increased by the action of 
pollen from a legitimate plant, but still did not reach the normal 
standard. 


Cuass LV. Illegitimate Plants raised from a Mid-styled 
Parent fertilised with pollen from own-form longest 
stamens. 


After two trials, I succeeded in raising only four 
plants from this illegitimate union. These proved to 
be three mid-styled and one long-styled; but from so 
small a number we can hardly judge of the tendency 
in mid-styled plants when self-fertilised to reproduce 
the same form. These four plants never attained their 
full and normal height; the long-styled plant had 
several of its anthers céntabescent. 

Plant 18. This mid-styled plant, when freely and legitimately 
fertilised during 1865 by illegitimate plants descended from 


self-fertilised long-, short-, and mid-styled plants, yielded an 
average from ten capsules of 102-6 seeds, with a maximum of 


198 ILLEGITIMATE OFFSPRING OF Cuap. V. 


131 and a minimum of 63: hence this plant did not produce 
quite 80 per cent. of the normal number of seeds. Twelve 
flowers were artificially and legitimately fertilised with pollen 
from a legitimate long-styled plant, and yielded from nine 
capsules an average of 1161 seeds, which.were finer than 
in the previous case, with a maximum of 135 and a minimum 
of 75; so that, as with Plant 17, pollen from a legitimate 
plant increased the fertility, but did not bring it up to the full 
standard. 

Plant 19. This mid-styled plant, fertilised in the same manner 
and at the same period as the last, yielded an average from 
ten capsules of 73°4 seeds, with a maximum of 87 and a mini- 
mum of 64: hence this plant produced only 56 per cent. of the 
full number of seeds. ‘Thirteen flowers were artificially and 
legitimately fertilised with pollen from a legitimate long-styled 
plant, and yielded ten capsules with an average of 95-6 seeds; 
so that the application of pollen from a legitimate plant added, 
as in the two previous cases, to the fertility, but did not bring 
it up to the proper standard. 

lant 20. This long-styled plant, of the same parentage with 
the two last mid-styled plants, and freely fertilised in the same 
manner, yielded an average from ten capsules of 69°6 seeds, 
with a maximum of 83 and a minimum of 52: hence this plant 
produced 75 per cent. of the full number of seeds. 


Ciass V. Illegitimate Plants raised from a Short-styled 
Parent fertilised with pollen from the mid-length 
stamens of the long-styled form. 


In the four previous classes, plants raised from the 
three forms fertilised with pollen from either the longer 
or shorter stamens of the same form, but generally not 
from the same plant, have been described. Six other 
illegitimate unions are possible, namely, between the 
three forms and the stamens in the other two forms 
which do not correspond in height with their pistils. 
But I succeeded in raising plants from only three of 
these six unions. From one of them, forming the pre- 
sent Class V., twelve plants were raised; these con- 
sisted of eight short-styled, and four long-styled plants, 


Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 199 


with not one mid-styled. These twelve plants never 
attained quite their full and proper height, but by no 
means deserved to be called dwarfs. The anthers in 
some of the flowers were contabescent. One plant was 
remarkable from all the longer stamens in every flower 
and from many of the shorter ones having their 
anthers in this condition. The pollen of four other 
plants, in which none of the anthers were contabe- 
scent, was examined; in one a moderate number of 
grains were minute and shrivelled, but in the other 
three they appeared perfectly sound. With respect to 
the power of producing seed, five plants (Nos. 21 to 
25) were observed: one yielded scarcely more than 
half the normal number; a second was slightly infer- 
tile; but the three others actually produced a larger 
average number of seeds, with a higher maximum, 
than the standard. In my concluding remarks I shall 
recur to this fact, which at first appears inexplicable. 


Plant 21. This short-styled plant, freely and legitimately 
fertilised during 1865 by illegitimate plants, descended from 
self-fertilised long-, mid- and short-styled parents, yielded an 
average from ten capsules of 43 seeds, with a. maximum of 63 
and a minimum of 26: hence this plant, which was the one 
with all its longer and many of its shorter stamens contabescent, 
produced only 52 per cent. of the proper number of seeds. 

Plant 22. This short-styled plant produced perfectly sound 
pollen, as viewed under the microscope. During 1866 it was 
freely and legitimately fertilised by other illegitimate plants 
belonging to the present and the following class, both of which 
include many highly fertile plants. Under these circumstances 
it yielded from eight capsules an average of 100°5 seeds, with 
a maximum of 123 and a minimum of 86; so that it produced 
121 per cent. of seeds in comparison with the normal standard. 
During 1864 it was allowed to be freely and legitimately ferti- 
lised by legitimate and illegitimate plants, and yielded an 
average, from eight capsules, of 104°2 seeds, with a maximum 
of 125 and a minimum of 90; consequently it exceeded the 
normal standard, producing 125 per cent. of seeds. In this 


200 ILLEGITIMATE OFFSPRING OF Cuap. V. 


case, as in some previous cases, pollen from legitimate plants 
added in a small degree to the fertility of the plant; and the 
fertility would, perhaps, have been still greater had not the 
summer of 1864 been very hot and certainly unfavourable to 
some of the plants of Lythrum. 

Plant 23. This short-styled plant produced perfectly sound 
pollen. During 1866 it was freely and legitimately fertilised by 
the other illegitimate plants specified under the last experi- 
ment, and eight capsules yielded an average of 113-5 seeds, 
with a maximum of 123 and a minimum of 93. Hence this 
plant exceeded the normal standard, producing no less than 136 
per cent. of seeds. 

Plant 24. This long-styled plant produced pollen which 
seemed under the microscope sound; but some of the grains 
did not swell when placed in water. During 1864 it was 
legitimately fertilised by legitimate and illegitimate plants in 
the same manner as Plant 22, but yielded an average, from ten 
capsules, of only 55 seeds, with a maximum of 88 and a mini- 
mum of 24, thus attaining 59 per cent. of the normal fertility. 
This low degree of fertility, I presume, was owing to the un- 
favourable season ; for during 1866, when legitimately fertilised 
by illegitimate plants in the manner described under No. 22, it 
yielded an average, from eight capsules, of 82 seeds, with a 
maximum of 120 and a minimum of 67, thus producing 88 per 
cent. of the normal number of seeds. 

Plant 25. The pollen of this long-styled plant contained a 
moderate number of poor and shrivelled grains; and this is a 
surprising circumstance, as it yielded an extraordinary number 
of seeds. During 1866 it was freely and legitimately fertilised 
by illegitimate plants, as described under No. 22, and yielded 
an average, from eight capsules, of 122-5 seeds, with a maximum 
of 149 and a minimum of 84. Hence this plant exceeded 
the normal standard, producing no less than 131 per cent. of 
seeds, 


Cuass VI. Illegitimate Plants raised from Mid-styled 
Parents fertilised with pollen from the shortest 
stamens of the long-styled form. 


IT raised from this union twenty-five plants, which 
proved to be seventeen long-styled and eight mid- 


Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 201 


styled, but not one short-styled. None of these plants 
were in the least dwarfed. I examined, during the 
highly favourable season of 1866, the pollen of four 
plants : in one mid-styled plant, some of the anthers of 
the longest stamens were contabescent, but the pollen- 
grains in the other anthers were mostly sound, as 
they were in all the anthers of the shortest stamens ; 
in two other mid-styled and in one long-styled plant 
many of the pollen-grains were small and shrivelled ; 
and in the latter plant as many as adifth or sixth part 
appeared to be in this state. I counted the seeds in 
five plants (Nos. 26 to 30), of which two were mode- 
rately sterile and three fully fertile. 


Plant 26. This mid-styled plant was freely and legitimately 
fertilised, during the rather unfavourable year 1864, by numer- 
ous surrounding legitimate and illegitimate plants. It yielded 
an average, from ten capsules, of 88°5 seeds, with a maximum 
of 110 and a minimum of 64, thus attaining 64 per cent. of the 
normal fertility. During the highly favourable year 1866, it 
was freely and legitimately fertilised by illegitimate plants 
belonging to the present Class and to Class V., and yielded 
an average, from eight capsules, of 86 seeds, with a maximum 
of 109 and a minimum of 61, and thus attained 66 per cent. 
of the normal fertility. This was the plant with some of the 
anthers of the longest stamens contabescent as above mentioned. 

Plant 27. This mid-styled plant, fertilised during 1864 in the 
same manner as the last, yielded an average, from ten capsules, 
of 99°4 seeds, with a maximum of 122 anda minimum of 53, 
thus attaining to 76 per cent. of the normal fertility. If the 
season had been more favourable, its fertility would probably 
have been somewhat greater, but, judging from the last experi- 
ment, only in a slight degree. 

Plant 28. This mid-styled plant, when legitimately fertilised 
during the favourable season of 1866, in the manner described 
under No. 26, yielded an average, from eight capsules, of 89 
seeds, with a maximum of 119 and a minimum of 69, thus pro- 
ducing 68 per cent. of the full number of seeds. In the pollen 
of both sets of anthers, nearly as many grains were small and 
shrivelled as sound. 


202 ILLEGITIMATE OFFSPRING OF Cuap. V. 


Plant 29. This long-styled plant was legitimately fertilised 
during the unfavourable season of 1864, in the manner described 
under No. .26, and yielded an average, from ten capsules, of 
84°6 seeds, with a maximum of 1382 and a minimum of 47, thus 
attaining to 91 per cent. of the normal fertility. During the 
highly favourable season of 1866, when fertilised in the manner 
described under No. 26, it yielded an average, from nine cap- 
sules (one poor capsule haying been excluded), of 100 seeds, 
with a maximum of 121 and a minimum of 77. This plant thus 
exceeded the normal standard, and produced 107 per cent. of 
seeds. In both sets of anthers there were a good many bad and 
shrivelled pollen-grains, but not so many as in the last-described 
plant. 

Plant 30. This long-styled plant was legitimately fertilised 
during 1866 in the manner described under No. 26, and yielded 
an average, from eight capsules, of 94 seeds, with a maximum 
of 106 and a minimum of 66; so that it exceeded the normal 
standard, yielding 101 per cent. of seeds. 

Plant 31. Some flowers on this long-styled plant were arti- 
ficially and legitimately fertilised by one of its brother illegiti- 
mate mid-styled plants; and five capsules yielded an average of 
90°6 seeds, with a maximum of 97 and a minimum of 79. 
Hence, as far as can be judged from so few capsules, this plant 
attained, under these favourable circumstances, 98 per cent. of 
the normal standard. 


Cuass VIL. Illegitimate Plants raised from Mid-styled 
Parents fertilised with pollen from the longest stamens 
of the short-styled form. 


It was shown in the last chapter that the union from 
which these illegitimate plants were raised is far more 
fertile than any other illegitimate union ; for the mid- 
styled parent, when thus fertilised, yielded an average 
(all very poor capsules being excluded) of 102°8 seeds, 
with a maximum of 130; and the seedlings in the 
present class likewise have their fertility not at all 
lessened. Forty plants were raised ; and these attained 
their full height and were covered with seed-capsules. 


Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 203 


Nor did I observe any contabescent anthers. It de- 
serves, also, particular notice that these plants, differ- 
ently from what occurred in any of the previous classes, 
consisted of all three forms, namely, eighteen short- 
styled, fourteen long-styled, and eight mid-styled 


_ plants. As these plants were so fertile, I counted the 


seeds only in the two following cases. 


Plant 32. This mid-styled plant was freely and legitimately 
fertilised during the unfavourable year of 1864, by numerous 
surrounding legitimate and illegitimate plants. Eight cap- 
sules yielded an average of 127-2 seeds, with a maximum of 144 
and a minimum of 96; so that this plant attained 98 per cent. 
of the normal standard. 

Plant 33. This short-styled plant was fertilised in the same 
manner and at the same time with the last; and ten capsules 
yielded an average of 113°9, with a maximum of 137 and a 
minimum of 90. Hence this plant produced no less than 1387 
per cent. of seeds in comparison with the normal standard. 


Concluding Remarks on the Illegitimate Offspring of the 
three forms of Lythrum salicaria. 


From the three forms occurring in approximately 
equal numbers in a state of nature, and from the re- 
sults of sowing seed naturally produced, there is reason 
to believe that each form, when legitimately fertilised, 
reproduces all three forms in about equal numbers. 
Now, we have seen (and the fact is a very singular 
one) that the fifty-six plants produced from the 
long-styled form, illegitimately fertilised with pollen 
from the same form (Class I. and II.), were all long- 
styled. The short-styled form, when self-fertilised 
(Class ILI.), produced eight short-styled and one long- 
styled plant; and the mid-styled form, similarly treated 
(Class IV.), produced three mid-styled and one long- 
styled offspring ; so that these two forms, when ille- 


204 ILLEGITIMATE OFFSPRING OF Cuar. V 


gitimately fertilised with pollen from the same form, 
evince a strong, but not exclusive, tendency to repro- 
duce the parent-form. When the short-styled form 
was illegitimately fertilised by the long-styled form 
(Class V.), and again when the mid-styled was illegiti- 
mately fertilised by the long-styled (Class VI.), in 
each case the two parent-forms alone were reproduced. 
As thirty-seven plants were raised from these two 
unions, we may, with much confidence, believe that it 
is the rule that plants thus derived usually consist of 
both parent-forms, but not of the third form. When, 
however, the mid-styled form was illegitimately fer- 
tilised by the longest stamens of the short-styled 
(Class VII.), the same rule did not hold good; for the 
seedlings consisted of all three forms. The illegiti- 
mate union from which these latter seedlings were 
raised is, as previously stated, singularly fertile, and 
the seedlings themselves exhibited no signs of sterility 
and grew to their full height. From the consideration 
of these several facts, and from analogous ones to be 
given under Oxalis, it seems probable that in a state 
of nature the pistil of each form usually receives, 
through the agency of insects, pollen from the stamens 
of corresponding height from both the other forms. 
But the case last given shows that the application of 
two kinds of pollen is not indispensable for the pro- 
duction of all three forms. Hildebrand has suggested 
that the cause of all three forms being regularly and 
naturally reproduced, may be that some of the flowers 
are fertilised with one kind of pollen, and others 
on the same plant with the other kind of pollen. 
Finally, of the three forms, the long-styled evinces 
somewhat the strongest tendency to reappear amongst 
the offspring, whether both, or one, or neither of the 
parents are long-styled. 


Pape 
Pe ee, a ee ——_— 


Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 205 


TABLE 30. 


Tabulated results of the fertility of the foregoing illegitimate 
plants, when legitimately fertilised, generally by illegitimate 
plants, as described under each experiment. Plants 11, 12 
and 138 are excluded, as they were illegitimately fertilised. 


Normal Standard of Fertility of the three forms, when legitimate’y 
and naturally fertilised. 


| Average Maximum 


Form Number of Number in| Minimum Number in any 
Seeds per | any one one Capsule. 
Capsule. | Capsule. 
eee ertsis +h = |{No record was kept, as 
Min-styled ; <« . -.|. 1380 151 all very poor capsules 
Short-styled . . . 83°5 112 were rejected. 


Cxass I. and I1.—ZTllegitimate Plants raised from Long-styled 
Parents fertilised with pollin from own-form mid-length or 
shortest stamens: 


“Average Num- 
Average |Maximum) Minimum _ ber of Seeds, 
Wuniber of Plant orn Number of Number in |Number in| expressed as 


Seeds per | any one any one the percentage 
Capsule. | Capsule. | Capsule. of the Normal 
| Standard. 
Plant 1. Long-styled 0 0 | 0 0 
a eae 59 4°5 ts 0 5 
7 ee - 4°5 ? 0 5 
pate » 4°5 ? 0 5 
ee 3 Oorl 2 0 Oorl 
= Aor 35 0 0 0) 0 
Oge am . 36°1 47 22 39 
et ns a 41:1 73 11 44 
(he or 57°1 86 23 61 
” 10 . . ” 44:2 | 69 | 


Cuass IlI.—Illegitimate Plants raised from Short-styled Parents 
Sertilised with pollen from own-form shortest stamens. 


51 | 11 | 35 


Plantl4 . . | Short-styled | 28°3 
ts.) a 32-6 49 a) ae 
poe: -3) 1%; - 77°8 97 60 | 94 
» 17. . | Long-styled | 76°3 88 57 82 


ae 


206 ILLEGITIMATE OFFSPRING OF Guar. V. 


TABLE 380—continued. 


Crass [V.—Jllegitimate Plants raised from Mid-styled Parents | 
fertilised with pollen from own-form longest stamens. 


Average Num- 

Average | Maximum | Minimum| ber of Seeds, 
Number of Number in|Number in| expressed as 
Seeds per | any one | any one |the percentage 

Capsule. | Capsule. | Capsule. jof the Normal | 
Standard. | 


Number of Plant. Form. 


——_—| 


Plant18 . . | Mid-styled. | 102°6 131 63 80 
Unig Oar? ‘ 73°4 87 64 56 
» 20. . | Long-styled 69°6 83 52 75 


Ciass V.—Zllegitimate Plants raised from Short-styled Parents 
fertilised with pollen from the mid-length stamens of the long- 
styled form. 


Plant 21 . . | Short-styled | 43:0 63 26 52 
ok ee x 100°5 | 123 86 121 
sary arse ti , 113°5 | 123 93 136 
»y 24. . | Long-styled | 82:0 120 67 88 
peas oe] 122°5 149 84 13 


” | 


Ciass VI.—Zllegitimate Plants raised from Mid-styled Parents 
fertilised with pollen from the shortest stamens of the long- 
styled form. 


Plant26 . . | Mid-styled. 86° 
9 . 


6+0 109 61 66 
Piao RON a 9°4 122 53 76 
SPE Stank Vic 5 89°0 119 69 68 
» 29. . | Long-styled | 100-0 121 77 107 
Mao ie. F 94+0 106 66 101 
i ee - 90°6 | 97 79 98 


Cuiass VII.—Jilegitimate Plants raised from Mid-styled Parents 
fertilised with pollen from the longest stamens of the short- 
styled form. 


Plant32 . . | Mid-styled. | 127°2 144 96 98 
eae < 2 Short-styled | 113-9 | 137 90 137 


Omar. V. HETEROSTYLED TRIMORPHIC PLANTS. 207 


The lessened fertility of most of these illegitimate 
plants is im many respects a highly remarkable phe- 
nomenon. ‘Thirty-three plants in the seven classes 
were subjected to various trials, and the seeds care- 
fully counted. Some of them were artificially ferti- 
lised, but the far greater number were freely fertilised 
(and this is the better and natural plan) through the 
agency of insects, by other illegitimate plants. In the 
right-hand, or percentage column, in the preceding 
table, a wide difference in fertility between the plants 
in the first four and the last three classes may be per- 
ceived. In the first four classes the plants are de- 
scended from the three forms illegitimately fertilised 
with pollen taken from the same form, but only 
rarely from the same plant. It is necessary to observe 
this latter circumstance; for, as I have elsewhere 
shown,* most plants, when fertilised with their own 
pollen, or that from the same plant, are in some 
degree sterile, and the seedlings raised from such 
unions are likewise in some degree sterile, dwarfed, 
and feeble. None of the nineteen illegitimate plants 
in the first four classes were completely fertile ; one, 
however, was nearly so, yielding 96 per cent. of the 
proper number of seeds. From this high degree of 
fertility we have many descending gradations, till we 
reach an absolute zero, when the plants, though bear- 
ing many flowers, did not produce, during successive 
years, a single seed or even seed-capsule. Some of the 
most sterile plants did not even yield a single seed 
when legitimately fertilised with pollen from legiti- 
mate plants. There is good reason to believe that the 
first seven plants in Class I. and IJ. were the offspring 


* <The Effects of Cross and Self-fertilisation in the Vegetable 
Kingdom,’ 1876, 


01 


208 ILLEGITIMATE OFFSPRING OF ~- Cnuap. V. 


of a long-styled plant fertilised with pollen from its 
own-form shortest stamens, and these plants were the 
most sterile of all. The remaining plants in Class I. 
and II. were almost certainly the product of pollen 
from the mid-length stamens, and although very ste- 
rile, they were less so than the first set. None of the 
plants in the first four classes attained their full and 
proper stature; the first seven, which were the most 
sterile of all (as already stated), were by far the most 
dwarfed, several of them never reaching to half their 
proper height. These same plants did not flower at so 
early an age, or at so early a period in the season, as 
they ought to have done. ‘The anthers in many of 
their flowers, and in the flowers of some other plants 
in the first six classes, were either contabescent or in- 
cluded numerous small and shrivelled pollen-grains. 
As the suspicion at one time occurred to me that the 
lessened fertility of the illegitimate plants might be 
due to the pollen alone haying been affected, I may 
remark that this certainly was not the case ; for several 
of them, when fertilised by sound pollen from legiti- 
mate plants, did not yield the full complement of 
seeds; hence it is certain that both the female and 
male reproductive organs were affected. In each of 
the seven classes, the plants, though descended from 
the same parents, sown at the same time and in the 
same soil, differed much in their average degree of 
fertility. 

Turning now to the fifth, sixth, and seventh classes, 
and looking to the right-hand column of the table, we © 
find nearly as many plants with a percentage of seeds 
above the normal standard as beneath it. As with 
most plants the number of seeds produced varies much, 
it might be thought that the present case was one 
merely of variability. But this view must be rejected, 


Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 209 


as far as the less fertile plants in these three classes 
are concerned: first, because none of the plants in 
Class V. attained their proper height, which shows 
that they were in some manner affected ; and, secondly, 
because many of the plants in Classes V. and VI. pro- 
duced anthers which were either contabescent or in- 
eluded small and shrivelled pollen-grains. And as in 
these cases the male organs were manifestly deterio- 
- rated, it is by far the most probable conclusion that 
the female organs were in some cases likewise affected, 
and that this was the cause of the reduced number of 
seeds. 

With respect to the six plants in these three classes 
which yielded a very high percentage of seeds, the 
thought naturally arises that the normal standard of 
fertility for the long-styled and short-styled forms 
(with which alone we are here concerned) may have 
been fixed too low, and that the six illegitimate plants 
are merely fully fertile. The standard for the long- 
styled form was deduced by counting the seeds in 
twenty-three capsules, and for the short-styled form 
from twenty-five capsules. I do not pretend that this 
is a sufficient number of capsules for absolute accu- 
racy ; but my experience has led me to believe that a 
very fair result may thus be gained. As, however, the 
maximum number observed in the twenty-five capsules 
of the short-styled form was low, the standard in this 
case may possibly be not quite high enough. But it 
should be observed, in the case of the illegitimate 
plants, that in order to avoid over-estimating their in- 
fertility, ten very fine capsules were always selected ; 
and the years 1865 and 1866, during which the plants 
in the three latter classes were experimented on, were 
highly favourable for seed-production. Now, if this 


210 ILLEGITIMATE OFFSPRING OF Cuar. V. 


plan of selecting very fine capsules during favourable. 
seasons had been followed for obtaming the normal 
standards, instead of taking, during various seasons, 
the first capsules which came to hand, the standards 
would undoubtedly have been considerably higher ; 
and thus the fact of the six foregoing plants appearing 
to yield an unnaturally high percentage of seeds may, 
perhaps, be explained. On this view, these plants are, 
in fact, merely fully fertile, and not fertile to an ab- 
normal degree. Nevertheless, as characters of all 
kinds are liable to variation, especially with organisms — 
unnaturally treated, and as in the four first and more 
sterile classes, the plants derived from the same pa- 
rents and treated in the same manner, certainly did 
vary much in sterility, it is possible that certain plants 
in the latter and more fertile classes may have varied 
so as to have acquired an abnormal degree of fertility. 
But it should be noticed that, if my standards err in 
being too low, the sterility of all the many sterile 
plants in the several classes will have to be estimated 
by so much the higher. Finally, we see that the ille- 
gitimate plants in the four first classes are all more or 
less sterile, some being absolutely barren, with one 
alone almost completely fertile; in the three latter 
classes, some of the plants are moderately sterile, 
whilst others are fully fertile, or possibly fertile in 
eXCess. 

The last point which need here be noticed is that, 
as far as the means of comparison serve, some degree 
of relationship generally exists between the infertility 
of the illegitimate union of the several parent-forms 
and that of their illegitimate offspring. Thus the 
two illegitimate unions, from which the plants in 
Classes VI. and VII. were derived, yielded a fair 
amount of seed, and only a few of these plants are in 


Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 211 


any degree sterile. On the other hand, the illegiti- 
mate unions between plants of the same form always 
yield very few seeds, and their seedlings are very 
sterile. Long-styled parent-plants when fertilised 
with pollen from their own-form shortest stamens, ap- 
pear to be rather more sterile than when fertilised with 
their own-form mid-length stamens ; and the seedlings 
from the former union were much more sterile than 
those from the latter union. In opposition to this re- 
lationship, short-styled plants illegitimately fertilised 
with pollen from the mid-length stamens of the long- 
styled form (Class V.) are very sterile; whereas some 
of the offspring raised from this union were far from 
being highly sterile. It may be added that there is a 
tolerably close parallelism in all the classes between 
the degree of sterility of the plants and their dwarfed 
stature. As previously stated, an illegitimate plant 
fertilised with pollen from a legitimate plant has its 
fertility slightly increased. The importance of the 
several foregoing conclusions will be apparent at the 
close of this chapter, when the illegitimate unions _be- 
tween the forms of the same species and their illegiti- 
mate offspring, are compared with the hybrid unions 
of distinct species and their hybrid offspring. 


OXALIS. 


No one has compared the legitimate and illegiti- 
mate offspring of any trimorphic species in this genus. 
Hildebrand sowed illegitimately fertilised seeds of 
Oxalis Valdiviana,* but they did not germinate; and 
this fact, as he remarks, supports my view that an 
illegitimate union resembles a hybrid one between 


* ‘Bot. Zeitung, 1871, p. 433, footnote. 


213 ILLEGITIMATE OFFSPRING OF Cuap. V. 


two distinct species, for the seeds in this latter case 
are often incapable of germination. 


The following observations relate to the nature of the forms 
which appear among the legitimate seedlings of Oxalis Valdiviana. 
Hildebrand raised, as described in the paper just referred to, 
211 seedlings from all six legitimate unions, and the three forms 
appeared among the offspring from each union. For instance, 
long-styled plants were legitimately fertilised with pollen from 
the longest stamens of the mid-styled form, and the seedlings 
consisted of 15 long-styled, 18 mid-styled, and 6 short-styled. 
We here see that a few short-styled plants were produced, though 
neither parent was short-styled; and so it was with the other 
legitimate unions. Out of the above 211 seedlings, 173 belonged 
to the same two forms as their parents, and only 38 belonged 
to the third form distinct from either parent. In the case of 
O. Regnelli, the result, as observed by Hildebrand, was nearly 
the same, but more striking: all the offspring from four of the 
legitimate unions consisted of the two parent-forms, whilst 
amongst the seedlings from the other two legitimate unions the 
third form appeared. Thus, of the 43 seedlings from the six 
legitimate unions, 35 belonged to the same two forms as their 
parents, and only 8 to the third form. Fritz Miiller also raised 
in Brazil] seedlings from long-styled plants of O. Regnelli legiti- 
mately fertilised with pollen from the longest stamens of the 
mid-styled form, and all these belonged to the two parent- 
forms.* Lastly, seedlings were raised by me from long-styled 
plants of O. speciosa legitimately fertilised by the short-styled 
form, and from the latter reciprocally fertilised by the long- 
styled; and these consisted of 33 long-styled and 26 short- 
styled plants, with not one mid-styled form. There can, there- 
fore, be no doubt that the legitimate offspring from any two 
forms of Oxalis tend to belong to the same two forms as their 
parents; but that a few seedlings belonging to the third form 
occasionally make their appearance; and this latter fact, as 
Hildebrand remarks, may be attributed to atavism, as some of 
their progenitors will almost certainly have belonged to the 
third form. 

When, however, any one form of Oxalis is fertilised ilegiti- 


* ¢ Jenaische Zeitschrift,’ &c. Band vi. 1871, p. 75. 


Carp. V. HETEROSTYLED DIMORPHIC PLANTS. 213 


mately with pollen from the same form, the seedlings appear to 
belong invariably to this form. Thus Hildebrand states* that 
long-styled plants of O. rosea growing by themselves have been 
propagated in Germany year after year by seed, and have always 
produced long-styled plants. Again, 17 seedlings were raised 
from mid-styled plants of O. hedysaroides growing by themselves, 
and these were all mid-styled. So that the forms of Oxalis, 
when illegitimately fertilised wth their own pollen, behave like 
the long-styled form of Lythrum salicaria, which when thus fer- 
tilised always produced with me long-styled offspring. 


PRIMULA. 
PRIMULA SINENSIS. 


I raised during February 1862, from some long- 
styled plants illegitimately fertilised with pollen from 
the same form, twenty-seven seedlings. These were 
all long-styled. They proved fully fertile or even 
fertile in excess; for ten flowers, fertilised with pollen 
from other plants of the same lot, yielded nine cap- 
sules, containing on an average 39°75 seeds, with a 
maximum in one capsule of 66 seeds. Four other 
flowers legitimately crossed with pollen from a legiti- 
mate plant, and four flowers on the latter crossed with 
pollen from the illegitimate seedlings, yielded seven 
capsules with an average of 53 seeds, with a maximum 
of 72. I must here state that I have found some 
difficulty in estimating the normal standard of fer- 
tility for the several unions of this species, as the 
results differ much during successive years, and 
the seeds vary so greatly in size that it is hard to 


* ‘Ueber den Trimorphismus zu Berlin,’ 21st June 1866, p. 373; 
in der Gattung Oxalis: Monats- and ‘ Bot. Zeitung,’ 1871, p. 435. 
berichte der Akad. der Wissen. 


214 ILLEGITIMATE OFFSPRING OF Cuar. V. 


decide which ought to be considered good. In order 
to avoid over-estimating the infertility of the several 
illegitimate unions, I have taken the normal standard 
as low as possible. 

From the foregoing twenty-seven illegitimate plants, 
fertilised with their own-form pollen, twenty-five seed- 
ling grandchildren were raised; and these were all 
long-styled; so that from the two illegitimate gene- 
rations fifty-two plants were raised, and all without 
exception proved long-styled. These grandchildren 
grew vigorously, and soon exceeded in height two 
other lots of illegitimate seedlings of different parent- 
age and one lot of equal-styled seedlings presently to 
be described. Hence I expected that they would have 
turned out highly ornamental plants; but when they 
flowered, they seemed, as my gardener remarked, to 
have gone back to the wild state; for the petals were 
pale-coloured, narrow, sometimes not touching each 
other, flat, generally deeply notched in the middle, 
but not flexuous on the margin, and with the yellow 
eye or centre conspicuous. Altogether these flowers 
were strikingly different from those of their pro- 
genitors; and this, I think, can only be accounted 
for on the principle of reversion. Most of the anthers 
on one plant were contabescent. Seventeen flowers 
on the grandchildren were illegitimately fertilised 
with pollen taken from other seedlings of the same 
lot, and produced fourteen capsules, containing on an 
average 29°2 seeds; but they ought to have con- 
tained about 85 seeds. Fifteen flowers legitimately 
fertilised with pollen from an illegitimate short-styled 
plant (belonging to the lot next to be described) pro- 
duced fourteen capsules, containing an average of 46 
seeds; they ought to have contained at least 50 seeds. 
Hence these grandchildren of illegitimate descent ap- 


Cuar. ¥. HETEROSTYLED DIMORPHIC PLANTS. 215 


pear to have lost, though only in a very slight degree, 
their full fertility. 

We will now turn to the short-styled form: from a, 
plant of this kind, fertilised with its own-form pollen, 
I raised, during February 1862, eight seedlings, seven 
of which were short-styled and one long-styled. They 
grew slowly, and never attained to the full stature of 
ordinary plants; some of them flowered precociously, 
and others late in the season. Tour flowers on these 
short-styled seedlings and four on the one long-styled 
seedling were illegitimately fertilised with their own- 
form pollen and produced only three capsules, con- 
taining on an average 23°6 seeds, with a maximum 
of 29; but we cannot judge of their fertility from so 
few capsules; and I have greater doubts about the 
normal standard for this union than about any other ; 
but I believe that rather above 25 seeds would be a 
fair estimate. Eight flowers on these same short-styled 
plants, and the one long-styled illegitimate plant 
were reciprocally and legitimately crossed; they pro- 
duced five capsules, which contained an average of 
28°6 seeds, with a maximum of 36. A reciprocal 
cross between legitimate plants of the two forms 
would have yielded an average of at least 57 seeds, 
with a possible maximum of 74 seeds; so that these 
illegitimate plants were sterile when legitimately 
crossed. 

I succeeded in raising from the above seven short- 
styled illegitimate plants, fertilised with their own- 
form pollen, only six plants—grandchildren of the 
first union. These, like their parents, were of low 
stature, and had so poor a constitution that four died 
before flowering. With ordinary plants it has been 
a rare eyent with me to have more than a single plant 
die out of a large lot. The two grandchildren which 


216 ILLEGITIMATE OFFSPRING OF Cuar. V 


lived and flowered were short-styled; and twelve of 
their flowers were fertilised with their own-form pollen 
and produced twelve capsules containing an average 
of 28:2 seeds; so that these two plants, though be- 
longing to so weakly a set, were rather more fertile 
than their parents, and perhaps not in any degree 
sterile. Jour flowers on the same two grandchildren 
were legitimately fertilised by a long-styled illegiti- 
mate plant, and produced four capsules, containing 
only 32°2 seeds instead of about 64 seeds, which is 
the normal average for legitimate short-styled plants 
legitimately crossed. 

By looking back, it will be seen that I raised at 
first from a short-styled plant fertilised with its own- 
form pollen one long-styled and seven short-styled 
illegitimate seedlings. These seedlings were legiti- 
mately intercrossed, and from their seed fifteen plants 
were raised, grandchildren of the first illegitimate 
union, and to my surprise all proved short-styled. 
Twelve short-styled flowers borne by these grand- 
children were illegitimately fertilised with pollen 
taken from other plants of the same lot, and produced 
eight capsules which contained an average of 21°8 
seeds, with a maximum of 35. These figures are 
rather below the normal standard for such a union. 
Six flowers were also legitimately fertilised with pollen 
from an illegitimate long-styled plant and produced 
only three capsules, containing on an average 23°6 
seeds, with a maximum of 35. Such a union in the 
case of a legitimate plant ought to have yielded an 
average of 64 seeds, with a possible maximum of 73 
seeds. 

Summary on the Transmission of Form, Constitution, 
and Fertility of the Illegitimate Offspring of Primula 
Stnensis.—In regard to the long-styled plants, their 


Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 217 


illegitimate offspring, of which fifty-two were raised in 
the course of two generations, were all long-styled.* 
These plants grew vigorously ; but the flowers in one 
instance were small, appearing as if they had reverted 
to the wild state. In the first illegitimate generation 
they were perfectly fertile, and in the second their 
fertility was only very slightly impaired. With 
respect to the short-styled plants, twenty-four out of 
twenty-five of their illegitimate offspring were short- 
styled. They were dwarfed in stature, and one lot of 
grandchildren had so poor a constitution that four out 
of six plants perished before flowermg. The two sur- 
vivors, when illegitimately fertilised with their own- 
form pollen, were rather less fertile than they ought 
to have been; but their loss of fertility was clearly 
shown in a special and unexpected manner, namely, 
when legitimately fertilised by other illegitimate 
plants: thus altogether eighteen flowers were fertilised 
in this manner, and yielded twelve capsules, which 
included on an average only 28°5 seeds, with a 
maximum of 45. Now a legitimate short-styled plant 
would have yielded, when legitimately fertilised, an 
ayerage of 64 seeds, with a possible maximum of 74. 
This particular kind of infertility will perhaps be best 
appreciated by a simile: we may assume that with 
mankind six children would be born on an average from 
an ordinary marriage ; but that only three would be 
born from an incestuous marriage. According to the 
analogy of Primula Sinensis, the children of such 


* Dr. Hildebrand, who first short-styled. From a short-styled 
ealled attention to this subject plant illegitimately fertilised with 
( Bot. Zeitung” 1864, p. 5), raised its own pollen he raised fourteen 
from a similar illegitimate union plants, of which eleven were short- 
seventeen plants, of which four- styled and three long-styled. 
teen were long-styled and three . 


218 ILLEGITIMATE OFFSPRING OF Cuar. V. 


incestuous marriages, if they continued to marry in- 
cestuously, would have their sterility only slightly 
increased ; but their fertility would not be restored by 
a proper marriage; for if two children, both of in- 
cestuous origin, but in no degree related to each 
other, were to marry, the marriage would of course be 
strictly legitimate, nevertheless they would not give 
birth to more than half the full and proper number 
of children. 


Eyual-styled variety of Primula Sinensis.—As any variation in 
the structure of the reproductive organs, combined with changed 


function, is a rare eyent, the following cases are worth giving. 


in detail. My attention was first called to the subject by ob- 
serving, in 1862, a long-styled plant, descended from a self- 
fertilised long-styled parent, which had some of its flowers in an 
anomalous state, namely, with the stamens placed low down in 
the corolla as in the ordinary long-styled form, but with the 
pistils so short that the stigmas stood on a level with the anthers. 
These stigmas were nearly as globular and as smooth as in the 
short-styled form, instead of being elongated .and rough as in 
the long-styled form. Here, then, we have combined in, the 
same flower, the short stamens of the long-styled form with a 
pistil closely resembling that of the short-styled form. But 
the structure varied much even on the same umbel: for in two 
flowers the pistil was intermediate in length between that of 
the Jong and that of the short-styled form, with the stigma 
elongated as in the former, and smooth as in the latter; and in 
three other flowers the structure was in all respects like that of 


the long-styled form. These modifications appeared to me so- 


remarkable that I fertilised eight of the flowers with their own 
pollen, and obtained five capsules, which contained on an aver- 
age 43 seeds; and this number shows that the flowers had 
become abnormally fertile in comparison with those of ordinary 
long-styled plants when self-fertilised. I was thus led to ex- 
amine the plants in several small collections, and the result 
showed that the equal-styled variety was not rare. 

In a state of nature the long and short-styled forms would no 
doubt occur in nearly equal numbers, as L infer from the analogy 
of the other heterostyled species of Primula, and from having 


— 


Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 219 


TABLE 31. 


Primula Sinensis, 


RTerAnrik Gener or Place: Long-styled | Short-styled | Equal-styled 


Form. Form. Variety. 

Men torwood 3, ) St 0 0 17 
OT) 20 0 9 
SOL) 5 Cae ae ir) 30 18 15 
2 eee 12 9 oe 
[JU ARIGE, seh esi Sime Sra 42 12 0 
ST JUS a 16 0 0 
DSS CGE HAI oe he eye su. eo vies 1 | 5 0 
My own plants from purchased seeds 13 7 0 

| | 51 43 


orale ee “ah 134 


raised the two forms of the present species in exactly the same 
number from flowers which had been J/eyitimately crossed. The 
preponderance in the above table of the long-styled form over 
the short-styled (in the proportion of 134 to 51) results from gar- 
deners generally collecting seed from self-fertilised flowers; and 
the long-styled flowers produce spontaneously much more seed 
(as shown in the first chapter) than the short-styled, owing to the 
anthers of the long-styled form being placed low down in the 
corolla, so that, when the flowers fall off, the anthers are dragged 
over the stigma; and we now also know that long-styled plants, 
when self-fertilised, very generally reproduce long-styled off- 
spring. From the consideration of this table, it occurred to 
me in the year 1862, that almost all the plants of the Chinese 
primrose cultivated in England would sooner or later become 
long-styled or equal-styled; and now, at the close of 1876, I 
have had five small collections of plants examined, and almost 
all consisted of long-styled, with some more or less well-cha- 
racterised equal-styled plants, but with not one short-styled. 
With respect to the equal-styled plants in the table, Mr. Hor- 
wood raised from purchased seeds four plants, which he re- 
membered were certainly not long-styled, but either short or 
equal-styled, probably the latter. These four plants were kept 
separate and allowed to fertilise themselves; from their seed the 
seventeen plants in the table were raised, all of which proved 
equal-styled. The stamens stood low down in the corolla as in 
the long-styled form ; and the stigmas, which were globular and 


220 ILLEGITIMATE OFFSPRING OF Cuar. V. 


smooth, were either completely surrounded by the anthers, or 
stood close above them. My son William made drawings for 
me, by the aid of the camera, of the pollen of one of the above 
equal-styled plants; and, in accordance with the position of the 
stamens, the grains resembled in their small size those of the 
long-styled form. He also examined pollen from two equal-styled 
plants at Southampton; and in both of them the grains dif- 
fered extremely in size in the same anthers, a large number 
being small and shrivelled, whilst many were fully as large as 
those of the short-styled form and rather more globular. It is 
probable that the large size of these grains was due, not to their 
having assumed the character of the short-styled form, but to 
monstrosity; for Max Wichura has observed pollen-grains of 
monstrous size in certain hybrids. The vast number of the 
small shrivelled grains in the above two cases explains the fact 
that, though equal-styled plants are generally fertile in a high 
degree, yet some of them yield few seeds. I may add that my 
son compared, in 1875, the grains from two white-flowered 
plants, in both of which the pistil projected above the anthers, 
but neither were properly long-styled or equal-styled; and in 
the one in which the stigma projected most, the grains were 
in diameter to those in the other plant, in which the stigma pro- 
jected less, as 100 to 88; whereas the difference between the 
grains from perfectly characterised long-styled and short-styled 
plants is as 100 to 57. So that these two plants were in an 
intermediate condition. To return to the 17 plants in the first 
line of Table 31: from the relative position of their stigmas and 
anthers, they-could hardly fail to fertilise themselves; and ac- 
cordingly four of them spontaneously yielded no less than 180 
capsules; of these Mr. Horwood selected eight fine capsules for 
sowing; and they included on an average 54°8 seeds, with a 
maximum of 72. He gave me thirty other capsules, taken | 
by hazard, of which twenty-seven contained good seeds, aver- 
aging 35°5, with a maximum of 70; but if six poor cap- 
sules, each with less than 13 seeds, be excluded, the average 
rises to 42°5. These are higher numbers than could be ex- 
pected from either well-characterised form if self-fertilised ; and 
this high degree of fertility accords with the view that the 
male organs belonged to one form, and the female organs par- 
tially to the other form; so that a self-union in the case of the 
equal-styled variety is in fact a legitimate union. 

The seed saved from the aboye seventeen self-fertilised equal- 


Cuarp. V. HETEROSTYLED DIMORPHIC PLANTS. 221 


styled plants produced sixteen plants, which all proved equal- 
styled, and resembled their parents in all the above-specified 
respects. The stamens, however, in one plant were seated higher 
up the tube of the corolla than in the true long-styled form ; 
in another plant almost all the anthers were contabescent. These 
sixteen plants were the grandchildren of the four original plants, 
which it is believed were equal-styled; so that this abnormal 
condition was faithfully transmitted, probably through three, 
and certainly through two generations. The fertility of one of 
these grandchildren was carefully observed: six flowers were 
fertilised with pollen from the same flower, and produced six 
capsules, containing on an average 68 seeds, with a maximum 
of 82, and a minimum of 40. Thirteen capsules spontaneously 
self-fertilised yielded an average of 53:2 seeds, with the astonish- 
ing maximum in one of 97 seeds. In no legitimate union has 
so high an average as 68 seeds been observed by me, or nearly 
so high a maximum as 82 and 97. These plants, therefore, not 
only have lost their proper heterostyled structure and peculiar 
functional powers, but have acquired an abnormal grade of fer- 
tility—unless, indeed, their high fertility may be accounted for 
by the stigmas receiving pollen from the circumjacent anthers 
at exactly the most favourable period. 

With respect to Mr. Duck’s lot in Table 31, seed was saved 
from a single plant, of which the form was not observed, 
and this produced nine equal-styled and twenty long-styled 
plants. The equal-styled resembled in all respects those pre- 
viously described; and eight of their capsules spontaneously 
self-fertilised contained on an average 44°4 seeds, with a 
maximum of 61 and a minimum of 23. In regard to the 
twenty long-styled plants, the pistil in some of the flowers did 
not project quite so high as in ordinary long-styled flowers; 
and the stigmas, though properly elongated, were smooth; so 
that we have here a slight approach in structure to the pistil of 
the short-styled form. Some of these long-styled plants also 
approached the equal-styled in function; for one of them pro- 
duced no less than fifteen spontaneously self-fertilised capsules, 
and of these eight contained, on an average, 31°7 seeds, with 
‘a maximum of 61. This average would be rather low for a 
long-styled plant artificially fertilised with its own pollen, but 
is high for one spontaneously self-fertilised. For instance, 
thirty-four capsules produced by the illegitimate grandchildren 
of a long-styled plant, spontaneously self-fertilised, contained 


222 | ILLEGITIMATE OFFSPRING OF Cuar. V. 


on an average only 9:1 seeds, with a maximum of 46. Some 
seeds indiscriminately saved from the foregoing twenty-nine 
equal-styled and long-styled plants produced sixteen seedlings, 
grandchildren of the original plant belonging to Mr. Duck; and 
these consisted of fourteen equal-styled and two long-styled 
plants ; and I mention this fact as an additional instance of the 
transmission of the equal-styled variety. 

The third lot in the table, namely the Baston plants, are the 
last which need be mentioned. The long and short-styled plants, 
and the fifteen equal-styled plants, were descended from two 
distinct stocks. The latter were derived from a single plant, 
which the gardener is positive was not long-styled; hence, pro- 
bably, it was equal-styled. In all these fifteen plants the anthers, 
occupying the same position as in the long-styled form, closely 
surrounded the stigma, which in onc instance alone was slightly 
elongated. Notwithstanding this position of the stigma, the 
flowers, as the gardener assured me, did not yield many seeds ; 
and this difference from the foregoing cases may perhaps have 
been caused by the pollen being bad, as in some of the South- 
ampton equal-styled plants. 


Conclusions with respect to the equal-styled variety of 
P. Sinensis.—That this is a variation, and not a third or 
distinct form, as in the trimorphic genera Lythrwm and 
Oxalis, is clear; for we have seen its first appearance 
in one out of a lot of illegitimate long-styled plants ; 
and in the case of Mr. Duck’s seedlings, long-styled 
plants, only slightly deviating from the normal state, 
as well as equal-styled plants were produced from the 
same self-fertilised parent. The position of the sta- 
mens in their proper place low down in the tube of the 
corolla, together with the small size of the pollen- 
grains, show, firstly, that the equal-styled variety is a 
modification of the long-styled form, and, secondly, that 
the pistil is the part which has varied most, as indeed 
was obvious in many of the plants. This variation is 
of frequent occurrence, and is strongly inherited when 
it has once appeared. It would, however, have pos- 


Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 223 


sessed little interest if it had consisted of a mere 
change of structure; but this is accompanied by modi- 
fied fertility. Its occurrence apparently stands in 
close relation with the illegitimate birth of the parent 
plant; but to this whole subject I shall hereafter 
recur. 

PRIMULA AURICULA. 


Although I made no experiments on the illegitimate offspring 
of this species, I refer to it for two reasons :—First, because 
I have observed two equal-styled plants in which the pistil 
resembled in all respects that of the long-styled form, whilst 
the stamens had become elongated as in the short-styled form, 
so that the stigma was almost surrounded by the anthers. The 
pollen-grains, however, of the elongated stamens resembled in 
_ their small size those of the shorter stamens proper to the long- 
styled form. Hence these plants have become equal-styled by 
the increased length of the stamens, instead of, as with P. 
Sinensis, by the diminished length of the pistil. Mr. J. Scott 
observed five other plants in the same state, and he shows * that 
one of them, when self-fertilised, yielded more seed than an 
ordinary long- or short-styled form would have done when 
similarly fertilised, but that it was far inferior in fertility to 
either form when legitimately crossed. Hence it appears that 
the male and female organs of this equal-styled variety have 
been modified in some special manner, not only in structure 
but in functional powers. This, moreover, is shown by the 
singular fact that both the long-styled and short-styled plants, 
fertilised with pollen from the equal-styled variety, yield a 
lower average of seed than when these two forms are fertilised 
with their own pollen. 

The second point which deserves notice is that florists always 
throw away the long-styled plants, and save seed exclusively 
from the short-styled form. Nevertheless, as Mr. Scott was 
informed by a man who raises this species extensively in Scot- 
land, about one-fourth of the seedlings appear long-styled; so 
that the short-styled form of the Auricula, when fertilised by 
its own pollen, does not reproduce the same form in so large a 
proportion as in the case of P. Sinensis. We may further infer 


* ‘Journal Proce. Linn. Soc.’ viii. (1864) p. 91. 


224 ILLEGITIMATE OFFSPRING OF Cuap. V. 


that the short-styled form is not rendered quite sterile by a 
long course of fertilisation with pollen of the same form: but as 
there would always be some liability to an occasional cross with 
the other form, we cannot tell how long self-fertilisation has 
been continued. 


PRIMULA FARINOSA. 


* Mr. Scott says * that it is not at all uncommon to find equal- 

styled plants of this heterostyled species. Judging from the 
size of the pollen-grains, these plants owe their structure, as in 
the case of P. auricula, to the abnormal elongation of the 
stamens of the long-styled form. . In accordance with this view, 
they yield Jess seed when crossed with the long-styled form 
than with the short-styled. But they differ in an anomalous 
manner from the equal-styled plants of P. awricula in being 
extremely sterile with their own pollen. 


PRIMULA ELATIOR. 


It was shown in the first chapter, on the authority of 
Herr Breitenbach, that equal-styled flowers are occasionally 
found on this species whilst growing in a state of nature; and 
this is the only instance of such an occurrence known to me, 
with the exception of some wild plants of the Oxlip—a hybrid 
between P. veris and vulgaris—which were equal-styled. Herr 
Breitenbach’s case is remarkable in another way; for equal- 
styled flowers were found in two instances on plants which bore 
both long-styled and short-styled flowers. In every other 
instance these two forms andthe equal-styled variety have been 
produced by distinct plants. 


PRIMULA VULGARIS, Brit. Fl. 


Var. acaulis of Linn. and P. acaulis of J acq. 


Var. rubra.—Mrz. Scott statest that this variety, which 
grew in the Botanic Garden in Edinburgh, was quite 
sterile when fertilised with pollen from the common 
primrose, as well as from a white variety of the same 


* “Journal Proc, Linn. Soc.’ viii. (1864), p. 115. 
¢ Ibid. p. 98. 


ae a ee 


| 


Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 225 


species, but that some of the plants, when artificially 
fertilised with their own pollen, yielded a moderate 
supply of seed. He was so kind as to send me some 
of these self-fertilised seeds, from which I raised the 
plants immediately to be described. I may premise 
that the results of my experiments on the seedlings, 
made on a large scale, do not accord with those by 
Mr. Scott on the parent-plant. 

First, in regard to the transmission of form and 
colour. The parent-plant was long-styled, and of a 
rich purple colour. From the self-fertilised seed 23 
plants were raised; of these 18 were purple of dif- 
ferent shades, with 2 of them a little streaked and 
freckled with yellow, thus showing a tendency to 
reversion; and 5 were yellow, but generally with a 
brighter orange centre than in the wild flower. All 
the plants were profuse flowerers. All were long- 
styled; but the pistil varied a good deal in length 
even on the same plant, being rather shorter, or con- 
siderably longer, than in the normal long-styled form ; 
and the stigmas likewise varied in shape. It is, 
therefore, probable that an equal-styled variety of the 
primrose might be found on careful search; and I 
have received two accounts of plants apparently in this 
condition. The stamens always occupied their proper 
position low down in the corolla; and the pollen- 
grains were of the small size proper to the long-styled 
form, but were mingled with many minute and 
shrivelled grains. The yellow-flowered and the purple- 
flowered plants of this first generation were fertilised 
under a net with their own pollen, and the seed sepa- 
rately sown. From the former, 22 plants were raised, 
and all were yellow and long-styled. Irom the latter 
or the purple-flowered plants, 24 long-styled plants 
were raised, of which 17 were purple and 7 yellow. 


226 ILLEGITIMATE OFFSPRING OF Cuar. V. 


In this last case we have an instance of reversion in 
colour, without the possibility of any cross, to the grand- 
parents or more distant progenitors of the plants in 
question. Altogether 23 plants in the first generation 
and 46 in the second generation were raised ; and the 
whole of these 69 illegitimate plants were long-styled ! 

Eight purple-flowered and two yellow-flowered plants 
of the first illegitimate generation were fertilised in 
various ways with their own pollen and with that of 
the common primrose; and the seeds were separately 
counted, but as I could detect no difference in fertility 
between the purple and yellow varieties, the results 
are run together in the following table. (See next 
page.) 

If we compare the figures in this table with those 
given in the first chapter, showing the normal fertility 
of the common primrose, we shall see that the illegiti- 
mate purple- and yellow- -flowered varieties are very 
sterile. For instance, 72 flowers were fertilised with 
their own pollen and produced only 11 good capsules ; 
but by the standard they ought to have produced 48 
capsules ; and each of these ought to have contained 
on an average 52:2 seeds, instead of only 115 seeds. 
When these plants were illegitimately and _ legiti- 
mately fertilised with pollen from the common prim- 


rose, the average numbers were increased, but were far | 


from attaining the normal standards. So it was when 
both forms of the common primrose were fertilised 
with pollen from these illegitimate plants; and this 
shows that their male as well as their female organs 
were ina deteriorated condition. The sterility of these 
plants was shown in another way, namely, by their not 
producing any capsules when the access of all insects 
(except such minute ones as Thrips) was prevented ; 
for under these circumstances the common long-styled 


gz 
} 
' 


. Tas.E 32. 


Nature of Plant experimented on, 
and kind of Union. 


Purple- and yellow-flowered illegi- 
timate long-styled plants, illegi-|) 
timately fertilised with pollen 
from the same = coe ee ae 5K 


Purple- and yellow-flowered Parle aad yliw-fomeetiog| 
timate long-styled plants, ier 


from the common long-styled 
primrose. . 
Or, if the ten poorest capsules, 


timately fertilised with “lal 


including less than 15 aa * 72 29 | 40°6 
| 


rejected, we get. 


Purple- and yellow-flowered illegi-) 
timate long-styled plants, /egi-| 
timately fertilised with pollen} 
from the common short-styled 
primrose. . 

Or, if the two poorest capsules, 
including less than 15 seeds, be 
rejected, we get. . . 

‘The long-styled form of the common) 
primrose, i/eyitimately fertilised | 
with pollen from the long-styled 
illegitimate purple- and yellow- 
flowered plants . 

Or, if the three poorest capsules 
be rejected, we get . . ‘} 


The short-styled form of the common) 
primrose, legitimately fertilised 
with pollen from the long-styled 
illegitimate purple- and yellow- 
flowered plants. . . . 


Number of 
Flowers fertilised. 


Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 


Primula vulgaris. 


T 

os be 

Beh 
SB |/8o. 
ae 5 eo 
975 |423 
a5 eae 

o 

Be | 225 
aa os 

g | 4 

oO 

1 Bt 
39 


26 18 36°4 
26 16 AE o2 
20 14 | 15°4 
20 II 18°9 
10 6 30°5 


227 


be oy < 
Hey Gs 
Bsa) Bs2 
S39 Aso 
axe)| Gee 
S|) ae 
ae) ae 
=| a 
26 5 
62 3 
62 18 
60 9 
60 15 
46 1 
46 8 
61 6 


a eT ily a a 


primrose produces a considerable number of capsules. 
There can, therefore, be no doubt that the fertility of 


228 ILLEGITIMATE OFFSPRING OF Cuap. V. 


these plants was greatly impaired. The loss is not 
correlated with the colour of the flower; and it was to 
ascertain this point that I made so many experiments. 
As the parent-plant growing in Edinburgh was found 
by Mr. Scott to be in a high degree sterile, it may 
have transmitted a similar tendency to its offspring, 
independently of their illegitimate birth. I am, how- 
ever, inclined to attribute some weight to the illegiti- 
macy of their descent, both from the analogy of other 
cases, and more especially from the fact that when the 
plants were legitimately fertilised with pollen of the 
common primrose they yielded an average, as may be 
seen in the table, of only 5 more seeds than when 
illegitimately fertilised with the same pollen. Now we 
know that it is eminently characteristic of the illegiti- 
mate offspring of Primula Sinensis that they yield but 
few more seeds when legitimately fertilised than when 
fertilised with their own-form pollen. 


PRIMULA VERIS, Brit. Fl. 
Var. officinalis of Linn., P. officinalis of Jacq. 


Seeds from the short-styled form of the cowslip 
fertilised with pollen from the same form germinate 
so badly that I raised from three successive sowings 
only fourteen plants, which consisted of nine short- 
styled and five long-styled plants Hence the short- 
styled form of the cowslip, when self-fertilised, does not 
transmit the same form nearly so truly as does that 
of P. Sinensis. From the long-styled form, always 
fertilised with its own-form pollen, I raised in the 
first generation three long-styled plants,—from their 
seed 53 long-styled grandchildren,—from their seed 
4 long-styled great-grandchildren,—from their seed 
20 long-styled great-great-grandchildren,—and lastly, 


—_ 


- Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 229 


from their seed 8 long-styled and 2 short-styled great- 
great-great-grandchildren. In this last generation 
short-styled plants appeared for the first time in the 
course of the six generations,—the parent long-styled 
plant which was fertilised with pollen from another 
plant of the same form being counted as the first 
generation. Their appearance may be attributed to 
atavism. From two other long-styled plants, fertilised 
with their own-form pollen, 72 plants were raised, 
which consisted of 68 long-styled and 4 short-styled. 
So that altogether 162 plants were raised from ille- 
gitimately fertilised long-styled cowslips, and these 
consisted of 156 long-styled and 6 short-styled plants. 

We will now turn to the fertility and powers of 
growth possessed by the illegitimate plants. From 
a short-styled plant, fertilised with its own-form 
pollen, one short-styled and two long-styled plants, 
and from a long-styled plant similarly fertilised three 
long-styled plants were at first raised. The fertility 
of these six illegitimate plants was carefully observed ; 
but I must premise that I cannot give any satisfactory 
standard of comparison as far as the number of the 
seeds is concerned; for though I counted the seeds 
of many legitimate plants fertilised legitimately and 
illegitimately, the number varied so greatly during 
successive seasons that no one standard will serve well 


- for illegitimate unions made during different seasons. 


Moreover the seeds in the same capsule frequently 
differ so much in size that it is scarcely possible 
to decide which ought to be counted as good seed. 
There remains as the best standard of comparison the 
proportional number of fertilised flowers which pro- 
duce capsules containing any seed. 

First, for the one illegitimate short-styled plant. 
In the course of three seasons 27 flowers were illegiti- 


230 ILLEGITIMATE OFFSPRING OF Cuap. V. 


mately fertilised with pollen from the same plant, and 
they. yielded only a single capsule, which, however, con- 
tained a rather large number of seeds for a union of 
this nature, namely, 25. As a standard of comparison 
I may state that during the same three seasons 44 
flowers borne by legitimate short-styled plants were 
self-fertilised, and yielded 26 capsules; so that the 
fact of the 27 flowers on the illegitimate plant having 
produced only one capsule proves how sterile it was. 
To show that the conditions of life were favourable, 
I will add that numerous plants of this and other 
species of Primula all produced an abundance of 
capsules whilst growing close by in the same soil with 
the present and following plants. The sterility of the 
above illegitimate short-styled plant depended on 
both the male and female organs being in a deterio- 
rated condition. This was manifestly the case with 
the pollen; for many of the anthers were shrivelled 
or contabescent. Nevertheless some of the anthers 
contained pollen, with which I succeeded in fertilising 
some flowers on the illegitimate long-styled plants 
immediately to be described. Four flowers on this 
same short-styled plant were likewise legitimately fer- 
tilised with pollen from one of the following long- 
styled plants; but only one capsule was produced, 
containing 26 seeds; and this is a very low number 
for a legitimate union. 

With respect to the five illegitimate long-styled 
plants of the first generation, derived from the above 
self-fertilised short-styled and long-styled parents, 
their fertility was observed during the same three 
years. These five plants, when self-fertilised, differed 
considerably from one ‘another in their degree of 
fertility, as was the case with the illegitimate long- 
styled plants of Lythrum salicaria ; and their fertility 


Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 231 


varied much according to the season. I may premise, 
as a standard of comparison, that during the same 
years 56 flowers on legitimate long-styled plants of 
the same age and grown in the same soil, were fer- 
tilised with their own pollen, and yielded 27 capsules ; 
that is, 48 per cent. On one of the five illegitimate 
long-styled plants 36 flowers were self-fertilised in 
the course of the three years, but they did not produce 
a single capsule. Many of the anthers on this plant 
were contabescent; but some seemed to contain 
sound pollen. Nor were the female organs quite 
impotent; for I obtained from a legitimate cross one 
capsule with good seed. On a second illegitimate 
long-styled plant 44 flowers were fertilised during the 
same years with their own pollen, but they produced 
only a single capsule. The third and fourth plants 
were in a very slight degree more productive. The 
fifth and last plant was decidedly more fertile; for 
42 self-fertilised flowers yielded 11 capsules. Alto- 
gether, in the course of the three years, no less than 
160 flowers on these five illegitimate long-styled 
plants were fertilised with their own pollen, but they 
yielded only 22 capsules. According to the standard 
above given, they ought to have yielded 80 capsules. 
These 22 capsules contained on an average 15-1 seeds. 
I believe, subject to the doubts before specified, that 
with legitimate plants the average number from a 
union of this nature would have been above 20 seeds. 
Twenty-four flowers on these same five _ illegitimate 
long-styled plants were legitimately fertilised with 
pollen from the above-described illegitimate short- 
styled plant, and produced only 9 capsules, which is 
an extremely small number for a legitimate union. 
These 9 capsules, however, contained an average of 38 
apparently good seeds, which is as large a number as 


11 


232 ILLEGITIMATE OFFSPRING OF Cuap. V. 


legitimate plants sometimes yield. But this high aver- 
age was almost certainly false; and I mention the case 
for the sake of showing the difficulty of arriving at a 
fair result ; for this average mainly depended on two 
capsules containing the extraordinary numbers of 7) _ 
and 56 seeds; these seeds, however, though I felt 
bound to count them, were so poor that, judging from 
trials made in other cases, I do not suppose that one 
would have germinated ; and therefore they ought not 
.to have been included. Lastly, 20 flowers were legiti- 
mately fertilised with pollen from a legitimate plant, 
and this increased their fertility; for they produced 
10 capsules. Yet this is but a very small proportion 
for a legitimate union. 

There can, therefore, be no doubt that these five 
long-styled plants and the one short-styled plant of 
the first illegitimate generation were extremely sterile. 
Their sterility was shown, as in the case of hybrids, 
in another way, namely, by their flowering profusely, 
and especially by the long endurance of the flowers. 
For instance, I fertilised many flowers on these plants, 
and fifteen days afterwards (viz. on March 22nd) I 
fertilised numerous long-styled and short-styled fiowers 
on common cowslips growing close by. These latter 
flowers, on April 8th, were withered, whilst most of the 
illegitimate flowers remained quite fresh for several 
days subsequently ; so that some of these illegitimate 
plants, after being fertilised, remained in full bloom 
for above a month. 

We will now turn to the fertility of the 53 illegiti- 
mate long-styled grandchildren, descended from the 
long-styled plant which was first fertilised with its 
own pollen. The pollen in two of these plants included 
a multitude of small and shrivelled grains. Never- 
theless they were not very sterile; for 25 flowers, fer- 


aa 


, Crap. V. HETEROSTYLED DIMORPHIC PLANTS. 233 


tilised with their own pollen, produced 15 capsules, 
containing an average of 16°3 seeds. As already 
stated, the probable average with legitimate plants 
for a union of this nature is rather above 20 seeds. 
These plants were remarkably healthy and vigorous, 
as long as they were kept under highly favourable 
conditions in pots in the greenhouse ; and such treat- 
ment greatly increases the fertility of the cowslip. 
When these same plants were planted during the next 
year (which, however, was an unfavourable one), out 
of doors in good soil, 20 self-fertilised flowers pro- 
duced only 5 capsules, containing extremely few and 
wretched seeds. 

Four long-styled great-grandchildren were raised 
from the self-fertilised grandchildren, and were kept 
under the same highly favourable conditions in the 
greenhouse; 10 of their flowers were fertilised with 
own-form pollen and yielded the large proportion of 6 
capsules, containing on an average 18°7 seeds. From 
these seeds 20 long-styled great-great-grandchildren 
were raised, which were likewise kept in the greenhouse. 
Thirty of their flowers were fertilised with their own 
pollen and yielded 17 capsules, containing on an aver- 
age no less than 32, mostly fine seeds. It appears, 
therefore, that the fertility of these plants of the fourth 
illegitimate generation, as long as they were kept 
under highly favourable conditions, had not decreased, 
but had rather increased. The result, however, was 
widely different when they were planted out of doors 
in good soil, where other cowslips grew vigorously and 
were completely fertile ; for these illegitimate plants 
now became much dwarfed in stature and extremely 
sterile, notwithstanding that they were exposed to the 
visits of insects, and must have been legitimately fer- 
tilised by the surrounding legitimate plants. A whole 


234 ILLEGITIMATE OFFSPRING OF Cuar. V. 


row of these plants of the fourth illegitimate genera- 
tion, thus freely exposed and legitimately fertilised, 
produced only 3 capsules, containing on an ayerage 
only 17 seeds. During the ensuing winter almost all 
these plants died, and the few survivors were miserably 
unhealthy, whilst the surrounding legitimate plants 
were not in the least injured. 

The seeds from the great-great-grandchildren were 
sown, and 8 long-styled and 2 short-styled plants of 
the fifth illegitimate generation raised. These whilst 
still in the greenhouse produced smaller leaves and 
shorter flower-stalks than some legitimate plants with 
which they grew in competition ; but it should be ob- 
served that the latter were the product of a cross with 
a fresh stock,—a circumstance which by itself would 
have added much to their vigour.* When these ille- 
gitimate plants were transferred to fairly good soil 
out of doors, they became during the two following 
years much more dwarfed in stature and produced very 
few flower-stems ; and although they must have been 
legitimately fertilised by insects, they yielded cap- 
sules, compared with those produced by the surround- 
ing legitimate plants, in the ratio only of 5 to 100! 
It is therefore certain that illegitimate fertilisation, 
continued during successive generations, affects the 
powers of growth and fertility of P. vers to an extra- 
ordinary degree ; more especially when the plants are 
exposed to ordinary conditions of life, instead of being 
protected in a greenhouse. 


Equal-styled red variety of P. veris—Mr. Scott has described + 
a plant of this kind growing in the Botanic Garden of Edin- 
burgh. He states that it was highly self-fertile, although insects 


* For full details of this ex- t ‘Proc. Linn. Soe.’ vol. viii. 
periment, see my ‘ Effects of Cross (1864), p. 105. 
and Self-fertilisation,’ 1876, p. 220, 


a 


Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 235 


were excluded; and he explains this fact by showing, first, that 
the anthers and stigma are in close apposition, and that the 
stamens in length, position and size of their pollen-grains 
resemble those of the short-styled form, whilst the pistil re- 
sembles that of the long-styled form both in length and in the 
structure of the stigma. Hence the self-union of this variety is, 
in fact, a legitimate union, and consequently is highly fertile. 
Mr. Scott further states that this variety yielded very few seeds 
when fertilised by either the long- or short-styled common 
cowslip, and, again, that both forms of the latter, when fertilised 
by the equal-styled variety, likewise produced very few seeds. 
But his experiments with the cowslip were few, and my results 
do not confirm his in any uniform manner. 

I raised twenty plants from self-fertilised seed sent me by Mr. 
Scott; and they all produced red flowers, varying slightly in 
tint. Of these, two were strictly long-styled both in structure ~ 
and in function; for their reproductive powers were tested by 
crosses with both forms of the common cowslip. Six plants 
were equal-styled; but on the same plant the pistil varied a 
good deal in length during different seasons. This was likewise 
the case, according to Mr. Scott, with the parent-plant. Lastly, 
twelve plants were in appearance short-styled; but they varied 
much more in the length of their pistils than ordinary short- 
styled cowslips, and they differed widely from the latter in 
their powers of reproduction. Their pistils had become short- 
styled in structure, whilst remaining long-styled in function. 
Short-styled cowslips, when insects are excluded, are extremely 
barren: for instance, on one occasion six fine plants produced 
only about 50 seeds (that is, less than the product of two good 
capsules), and on another occasion not a single capsule. Now, 
when the above twelve apparently short-styled seedlings were 
similarly treated, nearly all produced a great abundance of 
capsules, containing numerous seeds, which germinated re- 
markably well. Moreover three of these plants, which during 
the first year were furnished with quite short pistils, on the 
following year produced pistils of extraordinary length. The 
greater number, therefore, of these short-styled plants could not 
be distinguished in function from the equal-styled variety. The 
anthers in the six equal-styled and in the apparently twelve 
short-styled plants were seated high up in the corolla, as in the 
true short-styled cowslip; and the pollen-grains resembled 
those of the same form in their large size, but were mingled 


236 ILLEGITIMATE OFFSPRING OF Cuap. V. 


with a few shrivelled grains. In function this pollen was 
identical with that of the short-styled cowslip; for ten long- 
styled flowers of the common cowslip, legitimately fertilised 
with pollen from a true equal-styled variety, produced six cap- 
sules, containing on an average 34°4 seeds; whilst seven cap- 
sules on a short-styled cowslip illegitimately fertilised with 
pollen from the equal-styled variety, yielded an average of only 
14°5 seeds. 

As the equal-styled plants differ from one another in their 
powers of reproduction, and as this is an important subject, 
I will give a few details with respect to five of them. First, an 
equal-styled plant, protected from insects (as was done in all 
the following cases, with one stated exception), spontaneously 
produced numerous capsules, five of which gave an average of 
44°8 seeds, with a maximum in one capsule of 57. But six 
capsules, the product of fertilisation with pollen from a short- 
styled cowslip (and this is a legitimate union), gave an average 
of 28°5 seeds, with a maximum of 49; and this is a much lower 
average than might have been expected. Secondly, nine cap- 
sules from another equal-styled plant, which had not been 
protected from insects, but probably was self-fertilised, gave an 
average of 45°2 seeds, with a maximum of 58. Thirdly, another 
piant which had a very short pistil in 1865, produced spon- 
taneously many capsules, six of which contained an average of 
33°9 seeds, with a maximum of 388. In 1866 this same plant 
had a pistil of wonderful length; for it projected quite above 
the anthers, and the stigma resembled that of the long-styled 
form. In this condition it produced spontaneously a vast 
number of fine capsules, six of which contained almost exactly 
the same average number as before, viz. 84°3, with a maximum 


of 38. Four flowers on this plant, legitimately fertilised with 


pollen from a short-styled cowslip, yielded capsules with an 


average of 30°2 seeds. Fourthly another short-styled plant 


spontaneously produced in 1865 an abundance of capsules, ten 
of which contained an average of 35°6 seeds, with a maximum 
of 54. In 1866 this same plant had become in all respects long- 
styled, and ten capsules gave almost exactly the same average 
as before, viz. 85:1 seeds, with a maximum of 47. Eight 
flowers on this plant, legitimately fertilised with pollen from 
a short-styled cowslip, produced six capsules, with the high 
average of 53 seeds, and the high maximum of 67. Eight 
flowers were aiso fertilised with pollen from a long-styled cow- 


| 


Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 237 


slip (this being an illegitimate union), and produced seven 
capsules, containing an average of 24°4 seeds, with a maximum 
of 32. The fifth and last plant remained in the same condition 
during both years: it had a pistil rather longer than that of the 
true short-styled form, with the stigma smooth, as it ought to 
be in this form, but abnormal in shape, like a much-elongated 
inverted cone. It produced spontaneously many capsules, five 
of which, in 1865, gave an average of only 15°6 seeds; and in 
1866 ten capsules still gave an average only a little higher, viz. 
of 22-1, with a maximum of 30. Sixteen flowers were fertilised 
with pollen from a long-styled cowslip, and produced 12 cap- 
sules, with an average of 24:9 seeds, and a maximum of 42. 
Hight flowers were fertilised with pollen from a short-styled 
cowslip, but yielded only two capsules, containing 18 and 23 
seeds. Hence this plant, in function and partially in structure, 
was in an almost exactly intermediate state between the long- 
styled and short-styled form, but inclining towards the short- 
styled; and this accounts for the low average of seeds which it 
produced when spontaneously self-fertilised. ‘ 
The foregoing five plants thus differ much from one another in 
the nature of their fertility. In two individuals a great difference 
in the length of the pistil during two succeeding years made no 


~ difference in the number of seeds produced. As all five plants 


possessed the male organs of the short-styled form in a perfect 
state, and the female organs of the long-styled form in a more 
or less complete state, they spontaneously produced a surprising 
number of capsules, which generally contained a large average 
of remarkably fine seeds. With ordinary cowslips, legitimately 
fertilised, I once obtained from plants cultivated in the green- 
house the high average, from seven capsules, of 58:7 seeds, with 
a maximum in one capsule of 87 seeds; but from plants grown 
out of doors I never obtained a higher average than 41 seeds. 
Now two of the equal-styled plants, grown out of doors and 
spontaneously se/f-fertilised, gave averages of 44 and 45 seeds; 
but this high fertility may perhaps be in part attributed to the 
stigma receiving pollen from the surrounding anthers at exactly 
the right period. Two of these plants, fertilised with pollen 
from a short-styled cowslip (and this in fact is a legitimate 
union), gave a lower average than when self-fertilised. On the 
other hand, another plant, when similarly fertilised by a cowslip, 
yielded the unusually high average of 53 seeds, with a maximum 
of 67. Lastly, as we have just seen, one of these plants was in 


238 ILLEGITIMATE OFFSPRING OF Cuap. V. 


an almost exactly intermediate condition in its female organs 
between the long- and short-styled forms, and consequently, 
when self-fertilised, yielded a low average of seed. If we add 
together all the experiments which I made on the equal-styled 
plants, 41 spontaneously self-fertilised capsules (insects having 
been excluded) gave an average of 34 seeds, which is exactly the 
same number as the parent-plant yielded in Edinburgh. Thirty- 
four flowers, fertilised with pollen from the short-styled cowslip 
(and this is an analogous union), produced 17 capsules, contain- 
ing an average of 33°8 seeds. It is a rather singular cireum- 
stance, for which I cannot account, that 20 flowers, artificially fer- 
tilised on one occasion with pollen from the same plants yielded 
only ten capsules, containing the low average of 26-7 seeds. 

As bearing on inheritance, it may be added that 72 seed- 


lings were raised from one of the red-flowered, strictly equal- © 


styled, self-fertilised plants descended from the similarly cha- 
racterised Edinburgh plant. These 72 plants were there- 
fore grandchildren of the Edinburgh plant, and they all bore, 
as in the first generation, red flowers, with the exception of 
one plant, which reverted in colour to the common cowslip. 
In regard to structure, nine plants were truly long-styled 
and had their stamens seated low down in the corolla in the 
proper position; the remaining 63 plants were equal-styled, 
though the stigma in about a dozen of them stood a little below 
the anthers. We thus see that the anomalous combination in the 
same flower, of the male and female sexual organs which properly 
exist in the two distinct forms, was inherited with much force. 
Thirty-six seedlings were also raised from long and short-styled 
common cowslips, crossed with pollen from the equal-styled 
variety. Of these plants one alone was equal-styled, 20 were 
short-styled, but with the pistil in three of them rather too 
long, and the remaining 15 were long-styled. In this case we 
have an illustration of the difference between simple inheritance 
and prepotency of transmission; for the equal-styled variety, 
when self-fertilised, transmits its character, as we have just 
seen, with much force, but when crossed with the common 
cowslip cannot withstand the greater power of transmission 
of the latter. 


PULMONARIA. 


I have little to say on this genus. I obtained seeds of P. offi- 
cinalis from a garden where the long-styled form alone grew, 


ee 


Cuap. V. HETEROSTYLED PLANTS. 239 


and raised 11 geedlings, which were all long-styled. These 
plants were named for me by Dr. Hooker. They differed, as has 
been shown, from the plants belonging to this species which in 
Germany were experimented on by Hildebrand ;* for he found that 
the long-styled form was absolutely sterile with its own pollen, 
whilst my long-styled seedlings and the parent-plants yielded a 
fair supply of seed when self-fertilised. Plants of the long- 
styled form of Pulmonaria angustifolia were, like Hildebrand’s 
plants, absolutely sterile with their own pollen, so that I could 
neyer procure a single seed. On the other hand, the short- 
styled plants of this species, differently from those of P. off- 
cinalis, were fertile with their own pollen in a quite remarkable 
degree for a heterostyled plant. From seeds carefully self-fer- 
tilised I raised 18 plants, of which 13 proved short-styled and 
5 long-styled. 
POLYGONUM FAGOPYRUM. 
From flowers on long-styled plants fertilised illegitimately 
with pollen from the same plant, 49 seedlings were raised, and 
these consisted of 45-long-styled and 4 short-styled. From 
flowers on short-styled plants illegitimately fertilised with pollen 
from the same plant 33 seedlings were raised, and these con- 
sisted of 20 short-styled and 13 long-styled. So that the usual 
rule of illegitimately fertilised long-styled plants tending much 
more strongly than short-styled plants to reproduce their own 
form here holds good. The illegitimate plants derived from 
both forms flowered later than the legitimate, and were to the 
latter in height as 69 to 100. But as these illegitimate plants 
were descended from parents fertilised with their own pollen, 
whilst the legitimate plants were descended from parents crossed 
with pollen from a distinct individual, it is impossible to know 
how much of their difference in height and period of flowering, 
is due to the illegitimate birth of the one set, and how much 
to the other set being the product of a cross between distinct 
plants. 


Coneluding Remarks on the Illegitimate Offspring of 
Heterostyled Trimorphie and Dimorphie Plants. 


It is remarkable how closely and in how many points 
illegitimate unions between the two or three forms of the 


* * Bot. Zeitung, 1865, p. 13. 


240 ILLEGITIMATE OFFSPRING OF Cuar. V, 


same heterostyled species, together withetheir illegiti- 
mate offspring, resemble hybrid unions between distinct 
species together with their hybrid offspring. In both 
cases we meet with every degree of sterility, from very 
slightly lessened fertility to absolute barrenness, when 
not even a single seed-capsule is produced. In both 
cases the facility of effecting the first union is much 
influenced by the conditions to which the plants are 
exposed.* Both with hybrids and illegitimate plants 
the innate degree of sterility is highly variable in 
plants raised from the same mother-plant. In both 
cases the male organs are more plainly affected than 
the female; and we often find contabescent anthers 
enclosing shrivelled and utterly powerless pollen- 
grains. The more sterile hybrids, as Max Wichura 
has well shown,t are sometimes much dwarfed in 
stature, and have so weak a constitution that they are 
liable to premature death; and we have seen exactly 
parallel cases with the illegitimate seedlings of Lythrum 
and Primula. Many hybrids are the most persistent 
and profuse flowerers, as are some illegitimate plants. 
When a hybrid is crossed by either pure parent-form, 
it is notoriously much more fertile than when crossed 
inter se or by another hybrid ; so when an illegitimate 
plant is fertilised by a legitimate plant, it is more 
fertile than when fertilised inter se or by another ille- 
gitimate plant. When two species are crossed and 
they produce numerous seeds, we expect as a general 
rule that their hybrid offspring will be moderately 
fertile; but if the parent species produce extremely 
few seeds, we expect that the hybrids will be very 


* This has been remarked by chapter a striking illustration in 
many experimentalists in effecting the case of Primula veris. 
crosses between distinct species ; + ‘Die Bastardbefruchtung im 
and in regard to illegitimate Pflanzenreich,’ 1865. 
unions I have given in the first 


Cuar. V. HETEROSTYLED PLANTS. 241 


sterile. But there are marked exceptions, as shown 
by Gartner, to these rules. So it is with illegitimate 
unions and illegitimate offspring. Thus the mid- 
styled form of Lythrum salicaria, when illegitimately 
fertilised with pollen from the longest stamens of 
the short-styled form, produced an unusual number 
of seeds; and their illegitimate offspring were not at 
all, or hardly at all, sterile. On the other hand, the 
illegitimate offspring from the long-styled form, ferti- 
lised with pollen from the shortest stamens of the same 
form, yielded few seeds, and the illegitimate offspring 
thus produced were very sterile; but they were more 
sterile than might have been expected relatively to the 
difficulty of effecting the union of the parent sexual 
elements. No point is more remarkable in regard to 
the crossing of species than their unequal reciprocity. 
Thus species A will fertilise B with the greatest ease ; 
but B will not fertilise A after hundreds of trials. We 
have exactly the same case with illegitimate unions; 
for the mid-styled Lythrum salicaria was easily ferti- 
lised by pollen from the longest stamens of the short- 
styled form, and yielded many seeds; but the latter 
form did not yield a single seed when fertilised by the 
longest stamens of the mid-styled form. 

Another important point is prepotency. Gartner 
has shown that when a species is fertilised with pollen 
from another species, if it be afterwards fertilised with 
its own pollen, or with that of the same species, this 
is so prepotent over the foreign pollen that the effect 
of the latter, though placed on the stigma some time 
previously, is entirely destroyed. Exactly the same 
thing occurs with the two forms of a heterostyled 
species. Thus several long-styled flowers of Primula 
veris were fertilised illegitimately with pollen from 
another plant of the same form, and twenty-four hours 


242 ILLEGITIMATE OFFSPRING OF Cuar. V. 


afterwards legitimately with pollen from a short-styled 
dark-red polyanthus which is a variety of P. veris ; 
and the result was that every one of the thirty seed- 
lings thus raised bore flowers more or less red, show- 
ing plainly how prepotent the legitimate pollen from 
a short-styled plant was over the illegitimate pollen 
from a long-styled plant. 

In all the several foregoing points the parallelism is 
wonderfully close between the effects of illegitimate 
and hybrid fertilisation. It is hardly an exaggeration 
to assert that seedlings from an illegitimately fer- 
tilised heterostyled plant are hybrids formed within 
the limits of one and the same species. This conclu- 
sion is important, for we thus learn that the difficulty 
in sexually uniting two organic forms and the sterility 
of their offspring, afford no sure criterion of so-called 
specific distinctness. If any one were to cross two 
varieties of the same form of Lythrum or Primula for 
the sake of ascertaining whether they were specifically 
distinct, and he found that they could be united only 
with some difficulty, that their offspring were extremely 
sterile, and that the parents and their offspring re- 
sembled in a whole series of relations crossed species 
and their hybrid offspring, he might maintain that his 
varieties had been proved to be good and true species ; 
but he would be completely deceived. In the second 
place, as the forms of the same trimorphic or dimorphic 
heterostyled species are obviously identical in general 
structure, with the exception of the reproductive 
organs, and as they are identical in general constitu- 
tion (for they live under precisely the same condi- 
tions), the sterility of their illegitimate unions and 
that of their illegitimate offspring, must depend ex- 
clusively on the nature of the sexual elements and 
on their incompatibility for uniting in a particular 


i 


Cuar. V HETEROSTYLED PLANTS. 243 


manner. And as we have just seen that distinct species 
when crossed resemble in a whole series of relations the 
forms of the same species when illegitimately united, 
we are led to conclude that the sterility of the former 
must likewise depend exclusively on the incompatible 
nature of their sexual elements, and not on any general 
difference in constitution or structure. We are, indeed, 
led to this same conclusion by the impossibility of de- 
tecting any differences sufficient to account for certain 
species crossing with the greatest ease, whilst other 
closely allied species cannot be crossed, or can be crossed 
only with extreme difficulty. We are led to this con- 
clusion still more forcibly by considering the great 
difference which often exists in the facility of crossing 
reciprocally the same two species; for it is manifest in 
this case that the result must depend on the nature of 
the sexual elements, the male element of the one 
species acting freely on the female element of the 
other, but not so in a reversed direction. And now we 
see that this same conclusion is independently and 
strongly fortified by the consideration of the illegiti- 
mate unions of trimorphic and dimorphic heterostyled 
plants. In so complex and obscure a subject as hybrid- 
ism it is no slight gain to arrive at a definite conclu- 
sion, namely, that we must look exclusively to func- 
tional differences in the sexual elements, as the cause 
of the sterility of species when first crossed and of 
their hybrid offspring. It was this consideration which 
led me tomake the many observations recorded in this 
chapter, and which in my opinion make them worthy 
of publication. 


244 CONCLUDING REMARKS _ Cuap. VI. 


CHAPTER VI. 
ConcLUDING REMARKS ON HETEROSTYLED PLANTS. 


The essential character of heterostyled plants—Summary of the 
differences in fertility between legitimately and illegitimately fer- 
tilised plants—Diameter of the pollen-grains, size of anthers and 
structure of stigma in the different forms—Affinities of the genera 
which include heterostyled species—Nature of the advantages 
derived from heterostylism—The means by which plants became 
heterostyled—Transmission of form—Equal-styled varieties of 
heterostyled plants—Final remarks. — 


In the foregoing chapters all the heterostyled plants 
known to me have been more or less fully described. 
Several other cases have been indicated, especially by 
Professor Asa Gray and Kuhn,* in which the indi- 
viduals of the same species differ in the length of 
their stamens and pistils ; but as I have been often de- 
ceived by this character taken alone, it seems to me 
the more prudent course not to rank any species as 
heterostyled, unless we have evidence of more impor- 
tant differences between the forms, as in the diameter 
of the pollen-grains, or in the structure of the stigma. 
The individuals of many ordinary hermaphrodite plants 
habitually fertilise one another, owing to their male 
and female organs being mature at different periods, 
or to the structure of the parts, or to self-sterility, &c. ; 
and so it is with many hermaphrodite animals, for 
instance, land-snails or earth-worms ; but in all these 
cases any one individual can fully fertilise or be ferti- 


* Asa Gray, ‘American Journ. elsewhere as already referred to. 
of Science,’ 1865, p. 101; and Kuhn, ‘ Bot. Zeitung,’ 1867, p. 67. 


Cuar. VI. ON HETEROSTYLED PLANTS. 245 


lised by any other individual of the same species. This 
is not so with heterostyled plants: a long-styled, mid- 
styled or short-styled plant cannot fully fertilise or 
be fertilised by any other individual, but only by 
one belonging to another form. Thus the essen- 
tial character of plants belonging to the heterostyled 
class is that the individuals are divided into two or 
three bodies, like the males and females of dicecious 
plants or of the higher animals, which exist in approxi- 
mately equal numbers and are adapted for reciprocal 
fertilisation. The existence, therefore, of two or three 
bodies of individuals, differing from one another in the 
above more important characteristics, offers by itself 
good evidence that the species is heterostyled. But 
absolutely conclusive evidence can be derived only 
from experiments, and by finding that pollen must be 
applied from the one form to the other in order to 
ensure complete fertility. 

In order to show how much more fertile each form 
is when legitimately fertilised with pollen from the 
other form (or in the case of trimorphic species, with 
the proper pollen from one of the two other forms) 
than when illegitimately fertilised with its own-form 
pollen, I will append a Table (33) giving a summary 
of the results in all the cases hitherto ascertained. 
The fertility of the unions may be judged by two 
standards, namely, by the proportion of flowers which, 
when fertilised in the two methods, yield capsules, and 
by the average number of seeds per capsule. When 
_ there is a dash in the left-hand column opposite to 
the name of the species, the proportion of the flowers 
which yielded capsules was not recorded. 

The two or three forms of the same heterostyled 
species do not differ from one another in general habit 
or foliage, as sometimes, though rarely, happens with 


246 CONCLUDING REMARKS Cuar. VI. 


TABLE 33. 


Fertility of the Legitimate Unions taken together, compared with 
that of the Illegitimate Unions together. The fertility of the 
Legitimate Unions, as judged by both standards, is taken as 100. 


Illegitimate Unions. 
Proportional 

Name of Species, Number of Average 

Flowers Number of 

which pro- Seeds per 

duced Capsule. 
Capsules. 
Rrimulapveris se) ceisn (tats ese uane nls 69 65 
EO GEOR ede Pe MSs Or Oe eG) oats 27 75 
liberate omyamere Mee oe PamG. Saori bo: ta’ 60 54 
P. Sinensis eS etal) fedls 84 63 
P. Sinensis (second trial) priate ea ia, 0 53 
Po pimensis((ialdebrand)) 9.) st. ae) lie 100 42 
xray (Sea) oo Bo a oe 6G 80 15 
Pe OURKAMNENSIS Ae aits, We] foto eto sue iten ale 95 31 
Ps COMDUSOIAES | ered oe ve eaioeh ote® Jeratounts 74 66 
Pectin ahikowiey coe SG Go eo 72 48 
P. farinosa Aaa ; 71 44 
Average of the nine , species of Primula : 88°4 69 
Hottonia palustris (HeMhillen)\n sen ae — 61 
Linum grandiflorum (the difference ey pa 69 
is much STCAUCE) oe) eewie ° 5 iii 
L. perenne . ag dee Meigen tke | _— 20 
L. perenne (Hildebrand) ° 0 0 
Pulmonaria officinalis (German stock, Hilde- } 0 0 
brand). . om reer 4 toy PoP ph 

Pulmonaria angustifolia Bet msi Pe 35 32 
Mitchella repens. At : 20 47 
Borreria, Brazilian sp... : _ 0 
Polygonum fagopy RUNS Keer Vice er0 6 —— 46 
Lythrum salicaria. - = || 33 46 
Oxalis Valdiviana (Hildebrand). : - 2 34 
O, Regnelli “p 5. ape. 16 0 0 
OMEDECIOSA re) te owe, ie hs 15 49 


the two sexes of dicecious plants. Nor does the calyx 
differ, but the corolla sometimes differs slightly in shape, 
owing to the different position of the anthers. In Bor- 
reria the hairs within the tube of the corolla are differ- 
ently situated in the long-styled’and short-styled forms. 
In Pulmonaria there is a slight difference in the size of 


= 


Cuapr. VI. ON HETEROSTYLED PLANTS. 247 


the corolla, and in Pontederia in its colour. In the re- 
productive organs the differences are much greater and 
more important. In the one form the stamens may be 
all of the same length, and in the other graduated in 
length, or alternately longer and shorter. The fila- 
ments may differ in colons and thickness, and are 
sometimes nearly thrice as long in the one form as in the 
other. They adhere also for very different proportional 
lengths to the corolla. The anthers sometimes differ 
much in size in the two forms. Owing to the rotation 
of the filaments, the anthers, when mature, dehisce to- 
wards the circumference of the flower in one form of 
Faramea, and towards the centre in the other form. The 
pollen-grains sometimes differ conspicuously in colour, 
and often to an extraordinary degree in diameter. 
They differ also somewhat in shape, and apparently in 
their contents, as they are unequally opaque. In the 
short-styled form of Faramea the pollen-grains are 
covered with sharp points, so as to cohere readily to- 
gether or to an insect ; whilst the smaller grains of the 
long-styled form are quite smooth. 

With respect-to the pistil, the style may be almost 
thrice as long in the one form as in the other. In 
Oxalis it sometimes differs in hairiness in the three 
forms. In Linum the pistils either diverge and pass 
out between the filaments, or stand nearly upright and 
parallel to them. The stigmas in the two forms often 
differ much in size and shape, and more especially in 
the length and thickness of their papille; so that 
the surface may be rough or quite smooth. Owing to 
the rotation of the styles, the papillose surface of 
the stigma is turned outwards in one form of Linum 
perenne, and inwards in the other form. In flowers of 
the same age of Primula veris the ovules are larger in 
the long-styled than in the short-styled form. The 


248 CONCLUDING REMARKS Cuap. VI. 


seeds produced by the two or three forms often differ 
in number, and sometimes in size and weight; thus, 
five seeds from the long-styled form of Lythrum sali- 
carta equal in weight six from the mid-styled and 
seven from the short-styled form. Lastly, short-styled 
plants of Pulmonaria officinalis bear a larger number 
of flowers, and these set a larger proportional number 
of fruit, which however yield a lower average number 
of seed, than the long-styled plants. With hetero- 
styled plants we thus see in how many and in what 
important characters the forms of the same undoubted 
species often differ from one another—characters which 
with ordinary plants would be amply sufficient to dis- 
tinguish species of the same genus. 

As the pollen-grains of ordinary species belonging 
to the same genus generally resemble one another 
closely in all respects, it is worth while to show, in the 
following table (84), the difference in diameter be- 
tween the grains from the two or three forms of the 
same heterostyled species in the forty-three cases in 
which this was ascertained. But it should be observed 
that some of the following measurements are only 
approximately accurate, as only a few grains were 
measured. In several cases, also, the grains had been 
dried and were then soaked in water. Whenever they 
were of an elongated shape their longer diameters 
were measured. The grains from the short-styled 
plants are invariably larger than those from the long- 
styled, whenever there is any difference between them. 
The diameter of the former is represented in the table 
by the number 100. © 

We here see that, with seven or eight exceptions 
out of the forty-three cases, the pollen-grains from one 
form are larger than those from the other form of the 
same species. The extreme difference is as 100 to 55; 


Cuar. VI. ON HETEROSTYLED PLANTS. 249 


TABLE 34. 


Relative Diameter of the Pollen-grains from the forms of the same 
Heterostyled Species; those from the short-styled forin being 
represented by 100, 


Dimorphic Species. 


From the Long- From the Long- 
styled form. styled form. 
BTUMULAVENIS! ws Wyetté) 67 GCordiai(ep: 2) tacit «+ 129,100 
A ery 2 Gilia pulchella . . . . 100 
»  Sinensis(Hildebrand) 57 oy) MMicran bate, psn) tse 1. Ol 
apa pauricula;, .. -avibe it. Sethia acuminata! +2)... .. 983 
Hottonia palustris (H. Miiller) 61 Erythroxylum (sp.?) . . 93 
 Gself)) +2 64: Cratoxylon formosum . . 86 
Linum grandiflorum ., . 100 _ Mitchella repens,  pollen- 
- fay. 00 (2) grains of the long-styled 
riable), . a little smaller. 
SEHEMTM i svc. j2 100 Borneria (Spze)s ivy ich cn 
Pulmonaria officinalis . . 78 Faramea (sp.?) . 67 
angustifolia . 91 Suteria (sp. ?) (Fritz Maller 75 
Polygonum fagopyrum. . 82 Houstonia cerulea . . 72 
Leucosmia Burnettiana . 99 Oldenlandia (sp.?) . . . 78 
#giphilaelata. . . . 62 Hedyotis (sp. ?) . 88 
Menyanthes trifoliata . . 84 Coccocypselum (sp. 2 w 100 
Limnanthemum Indicum . 100 Mullen) iis. tert 2 
Walersa(ep.?).. . . 75 Lipostoma (sp.?) . . . 80 
Forsythia suspensa. . . 94 Cinchona micrantha . . 91 


Trimorphic Species. 


Ratio expressing the extreme differences | Ratio between the diameters of the pollen- 


in diameter of the pollen-grains fromthe | grains of the two sets of anthers in the 
two sets of anthers in the three forms. same form. 
Lythrum salicaria. .°. . 60 | Oxalis rosea, long-styled form 83 
Nesza verticillata. . 65 (Hildebrand) . : 
Oxalis Valdiviana (Hildebrand) 71 », compressa, short-styled 83 
oa 
PeePTICLIT, 5's) gt oO form. . 
3) Bpeciosa. «6. «6. Cw «COwSCOG9) | Pontederia (Gp-?) short-styled 87 
» Sensitiva . . . . 84 | fOTTH 3 pes 
Pontederia (sp.?) . . . . 55] “ other sp. smid-sty led 86 
forms; 


and we should bear in mind that in the case of 
spheres differing to this degree in diameter, their 
contents differ in the ratio of six to one. With all 
the species in which the grains differ in diameter, 
there is no exception to the rule that those from the 


250 CONCLUDING REMARKS Cuap. VI. 


anthers of the short-styled form, the tubes of which 
have to penetrate the longer pistil of the long-styled 
form, are larger than the grains from the other form. 
This curious relation led Delpino* (as it formerly did 
me) to believe that the larger size of the grains in 
the short-styled flowers is connected with the greater 
supply of matter needed for the development of their 
longer tubes. But the case of Linum, in which 
the grains of the two forms are of equal size, whilst 
the pistil of the one is about twice as long as that 
of the other, made me from the first feel very 
doubtful with respect to this view. My doubts have 
since been strengthened by the cases of Limnanthe- 
mum and Coccocypselum, in which the grains are of 
equal size in the two forms; whilst in the former 
genus the pistil is nearly thrice and in the latter 
twice as long as in the other form. In those species 
in which the grains are of unequal size in the two 
forms, there is no close relationship between the de- 
gree of their inequality and that of their pistils. 
Thus in Pulmonaria officinalis and in Erythroxy- 
lum the pistil in the long-styled form is about 
twice the length of that im the other form, whilst in 
the former species the pollen-grains are as 100 to 
78, and in the latter as 100 to 95 in diameter. In 
the two forms of Suteria the pistil differs but little 
in length, whilst the pollen - grains are as 100 to 
75 in diameter. These cases seem to prove that the 
difference in size between the grains in the two 
forms is not determined by the length of the pistil, 
down which the tubes have to grow. That with 
plants in general there is no close relationship between 


* «Sull’ Opera, la Distribuz:one dei Sessi nelle Picnte,’ &e., 1867, 
p- 17. , 


Cuapr. VI. ON HETEROSTYLED PLANTS. 251 


the size of the pollen-grains and the length of the 
pistil is manifest: for instance, I found that the dis- 
tended grains of Datura arborea were *00243 of an 
inch in diameter, and the pistil no less than 9°25 
inches in length; now the pistil in the small flowers 
of Polygonum fagopyrum is very short, yet the larger 
pollen-grains from the short-styled plants had exactly 
the same diameter as those from the Datura, with its 
enormously elongated pistil. 

Notwithstanding these several considerations, it is 
difficult quite to give up the belief that the pollen-grains 
from the longer stamens of heterostyled plants have 
become larger in order to allow of the development ot 
longer tubes; and the foregoing opposing facts may 
possibly be reconciled in the following manner. The 
tubes are at first developed from matter contained 
within the grains, for they are sometimes exserted 
to a considerable length, before the grains have 
touched the stigma; but botanists believe that they 
afterwards draw nourishment from the conducting 
tissue of the pistil. It is hardly possible te doubt 
that this must occur in such cases as that of the Da- 
tura, in which the tubes have to grow down the whole 
length of the pistil, and therefore to a length equal- 
ling 3,806 times the diameter of the grains (namely, 
*00245 of an inch) from which they are protruded. 
I may here remark that I have seen the pollen-grains 
of a willow, immersed in a very weak solution of honey, 
protrude their tubes, in the course of twelve hours, to 
a length thirteen times as great as the diameter of the 
grains. Now if we suppose that the tubes in some 
heterostyled species are developed wholly or almost 
wholly from matter contained within the grains, while 
in other species from matter yielded by the pistil, we 
ean see that in the former case it would be necessary 


252 CONCLUDING REMARKS Cuap. VI. 


that the grains of the two forms should differ in size 
relatively to the length of the pistil which the tubes 
have to penetrate, but that in the latter case 1t would 
not be necessary that the grains should thus differ. 
Whether this explanation can be considered satisfac- 
tory must remain at present doubtful. 

There is another remarkable difference between the 
forms of several heterostyled species, namely in the 
anthers of the short-styled flowers, which contain the 
larger pollen-grains, being longer than those of the 
long-styled flowers. This is the case with Hottonia 
palustris in the ratio of 100 to 83. With Limnan- 
themum Indicum the ratio is as 100 to 70. With the 
allied Menyanthes the anthers of the short-styled form 
are a little and with Villarsia conspicuously larger 
than those of the long-styled. With Pulmonaria 
angustifolia they vary much in size, but from an 
average of seven measurements of each kind the ratio 
is as 100 to 91. In six genera of the Rubiacez there 
is a similar difference, either slightly or well marked. 
Lastly, in the trimorphic Pontederia the ratio is 100 
to 88; the anthers from the longest stamens in the 
short-styled form being compared with those from the 
shortest stamens in the long-styled form. On the 
other hand, there is a similar and well-marked differ- 
ence in the length of the stamens in the two forms 
of Forsythia suspensa and of Innum flavum ; but in 
these two cases the anthers of the short-styled flowers 
are shorter than those of the long-styled. The rela- 
tive size of the anthers was not particularly attended 
to in the two forms of the other heterostyled plants, 
but I believe that they are generally equal, as is 
certainly the case with those of the common primrose 
and cowslip. 

The pistil differs in length in the two forms of every 


Cuar. VI. ON HETEROSTYLED PLANTS. 253 


heterostyled plant, and although a similar difference 
is very general with the stamens, yet in the two 
forms of Linum grandiflorum and of Cordia they are 
equal. There can hardly be a doubt that the rela- 
tive length of these organs is an adaptation for the 
safe transportal by insects of the pollen from the one 
form to the other. The exceptional cases in which 
these organs do not stand exactly ona level in the two 
forms may probably be explained by the manner in 
which the flowers are visited. With most of the 
species, if there is any difference in the size of the 
stigma in the two forms, that of the long-styled, what- 
ever its shape may be, is larger than that of the short- 
styled. But here again there are some exceptions to 
the rule, for in the short-styled form of Leucosmia 
Burnettiana the stigmas are longer and much narrower 
than those of the long-styled ; the ratio between the 
lengths of the stigmas in the two forms being 100 to 60. 
In the three Rubiaceous genera, Faramea, Houstonia 
and Oldenlandia, the stigmas of the short-styied form 
are likewise somewhat longer and narrower; and in 
the three forms of Owalis sensitiva the difference is 
strongly marked, for if the length of the two stigmas 
of the long-styled pistil be taken as 100, it will be 
represented in the mid- and short-styled forms by 
the numbers 141 and 164. As in all these cases the 
stigmas of the short-styled pistil are seated low down 
within a more or less tubular corolla, it is probable 
that they are better fitted by being long and narrow 
for brushing the pollen off the inserted proboscis of 
an insect. 

With many heterostyled plants the stigma differs 
in roughness in the two forms, and when this is the 
case there is no known exception to the rule that the 
papillz on the stigma of the long-styled form are longer 


254 CONCLUDING REMARKS Cuap. VL 


and often thicker than those on that of the short- 
styled. For instance, the papille on the long-styled 
stigma of Hottonia palustris are more than twice the 
length of those in the other form. This holds good 
even in the case of Houstonia coerulea, in which the 
stigmas are much shorter and stouter in the long- 
styled than in the short-styled form, for the papille 
on the former compared with those on the latter are 
as 100 to 58 in length. The length of the pistil 
in the long-styled form of Linwm grandiflorum varies 
much, and the stigmatic papille vary in a corre- 
sponding manner. From this fact I inferred at first 
that in all cases the difference in length between the 
stigmatic papille in the two forms was one merely of 
correlated growth ; but this can hardly be the true or 
general explanation, as the shorter stigmas of the 
long-styled form of Houstonia have the longer papilla. 
It is a more probable view that the papille, which 
render the stigma of the long-styled form of various 
species rough, serve to entangle effectually the large- 
sized pollen-grains brought by insects from the short- 
styled form, thus ensuring its legitimate fertilisation. 
This view is supported by the fact that the pollen- 
grains from the two forms of eight species in Table 
34 hardly differ in diameter, and the papille on their 
stigmas do not differ in length. 


The species which are at present positively or 
almost positively known to be heterostyled belong, as 
shown in the following table, to 58 genera, widely dis- 
tributed throughout the world. These genera are 
included in fourteen Families, most of which are very 
distinct from one another, for they belong to nine of 
the several great Series, into which phanerogamic 
plants have been divided by Bentham and Hooker. 


Cuar. VI. ON HETEROSTYLED PLANTS. 255 


TABLE 35. 
List of Genera including [eterostyled Species. 


DicoryLepons. DICOTYLEDONS. 
Cratoxylon. Hypericiner, | —“Mitchella. Rubiacez. 
Erythroxylum. LErythroxyler. | Diodia. oe 
Sethia. Fe Borreria, “~ 
Linum. Geraniacex. Spermacoce. 5 
Oxalis. es | Primula. Primulacee. 
Lythrum. Lythracee. Hottonia. ” 
Nesea. 5 Androsace. 5 
Cinchona. Rubiacez. Forsythia. Oleacex 
Bouvardia, “A | Menyanthes. Gentianacez. 
Manettia. |  Limnanthemum. s 
Hedyotis. 5s | Villarsia. F 
Oldenlandia. a |  Gilia. Polemoniacez. 
Houstonia. zs |  Cordia. Cordiez. 
Coccocypselum. - | Pulmonaria. Boraginez. 
Lipostoma. 59 |  giphila. Verbenacez. 
Knoxia. 5s Polygonum, Polygonee. 
Faramea. = Thymelea. Thymelez, 
Psychotria. ay 
Rudgea. . MONOCOTYLEDONS. 
Suteria. “A |  Pontederia. Pontederiacez, 


In some of these families the heterostyled condition 
must have been acquired at a very remote period. 
Thus the three closely allied genera, Menyanthes, 
Limnanthemum, and Villarsia, inhabit respectively 
Europe, India, and South America. Heterostyled 
species of Hedyotis are found in the temperate regions 
of North and the tropical regions of South America. 
Trimorphic species of Oxalis live on both sides of 
the Cordillera in South America and at the Cape of 
Good Hope. In these and some other cases it is not 
probable that each species acquired its heterostyled 
structure independently of its close allies. If they 
did not do so, the three closely connected genera of 
the Menyanthez and the several trimorphie species of 
Oxalis must have inherited their structure from a 
common progenitor. But an immense lapse of time 
will haye been necessary in all such cases for the 
modified descendants of a common progenitor to have 

12 


256 CONCLUDING REMARKS Cuar. VI. 


spread from a single centre to such widely remote and 
separated areas. The family of the Rubiaceze contains 
not far short of as many heterostyled genera as all 
the other thirteen families together; and hereafter 
ne doubt other Rubiaceous genera will be found to 
be heterostyled, although a large majority are homo- 
styled. Several closely allied genera in this family 
probably owe their heterostyled structure to descent 
in common; but as the genera thus characterised are 
distributed in no less than eight of the tribes into 
which this family has been divided by Bentham and 
Hooker, it is almost certain that several of them 
must have become heterostyled independently of 
one another. What there is in the constitution or 
structure of the members of this family which favours 
their becoming heterostyled, I cannot conjecture. 
Some families of considerable size, such as the Bo- 
raginee and Verbenace, include, as far as is at 
present known, only a single heterostyled genus, 
Polygonum also is the sole heterostyled genus in its 
family; and though it is a very large genus, no other 
species except P. fagopyrum is thus characterised. We 
may suspect that it has become heterostyled within 
a comparatively recent period, as it seems to be less 
strongly so in function than the species in any other 
genus, for both forms are capable of yielding a con- 
siderable number of spontaneously self-fertilised seeds. 
Polygonum in possessing only a single heterostyled 
species is an extreme case; but every other genus of 
considerable size which includes some such species 
likewise contains homostyled species. Lythrum in- 
cludes trimorphic, dimorphic, and homostyled species. 

Trees, bushes, and herbaceous plants, both large 
and small, bearing single flowers or flowers in dense 
spikes or heads, have been rendered heterostyled. 


Cuap. VI. ON HETEROSTYLED PLANTS. O57 


So have plants which inhabit alpine and lowland sites, 
dry land, marshes and water.* 

When I first began to experimentise on hetero- 
styled plants it was under the impression that they 
were tending to become dicecious ; but I was soon forced 
to relinquish this notion, as the long-styled plants of 
Primula which, from possessing a longer pistil, larger 
stigma, shorter stamens with smaller pollen-grains, 
seemed to be the more feminine of the two forms, 
yielded fewer seeds than the short-styled plants which 
appeared to be in the above respects the more mascu- 
line of the two. Moreover, trimorphic plants evidently 
come under the same category with dimorphic, and 
the former cannot be looked at as tending to become 
dicecious. With Lythrum salicaria, however, we have 
the curious and unique case of the mid-styled form 
being more feminine or less masculine in nature than 
the other two forms. This is shown by, the large 


* Out of the 38 genera known 
to include heterostyled species, 
about eight, or 21 per cent., are 
more or less aquatic in their 
habits. I was at first struck with 
this fact, for I was not then aware 
how large a proportion of or- 
dinary plants inhabit such sta- 
tions. Heterostyled plants may 
be said in one sense to have their 
sexes separated, as the forms must 
mutually fertilise one another. 
Therefore it seemed worth while 
to ascertain what proportion of 
the genera in the Linnean classes, 
Monecia, Dicecia and Poly- 
yamia, contained species which 
live ‘“‘in water, marshes, bogs or 
watery places.” In Sir W. J. 
Hooker’s ‘British Flora’ (4th 
edit. 1838) these three Linnean 
classes include 40 genera, 17 of 


which (i.e. 43 per cent.) contain 
species inhabiting the just-speci- 
fied stations. So that 43 per cent. 
of those British plants which 
have their sexes separated are 
more or less aquatic in their 
habits, whereas only 21 per cent. 
of heterostyled plants have such 
habits. I may add that the her- 
maphrodite classes, from Monan- 
dria to Gynandria inclusive, con- 
tain 447 genera, of which 113 are 
aquatic in the above sense, or only 
25 per cent. It thus appears, as 
far as can be judged from such 
imperfect data, that there is some 
connection between the separation 
of the sexes in plants and the 
watery nature of the sites which 
they inhabit; but that this does 
not hold good with heterostyled 
species. 


258 CONCLUDING REMARKS Cuar. VI. 


number of seeds which it yields in whatever manner 
it may be fertilised, and by its pollen (the grains of 
which are of smaller size than those from the corre- 
sponding stamens in the other two forms) when 
applied to the stigma of any form producing fewer 
seeds than the normal number. If we suppose the 
process of deterioration of the male organs in the mid- 
styled form to continue, the final result would be the 
production of a female plant; and Lythrum salicaria 
would then consist of two heterostyled hermaphrodites 
and a female. No such case is known to exist, but it 
is a possible one, as hermaphrodite and female forms 
of the same species are by no means rare. Although 
there is no reason to believe that heterostyled plants 
are regularly becoming dicecious, yet they offer sin- 
gular facilities, as will hereafter be shown, for such 
conversion ; and this appears occasionally to have been 
effected. 
We may feel sure that plants have been rendered 
heterostyled to ensure cross-fertilisation, for we now 
know that a cross between the distinct individuals of 
the same species is highly important for the vigour and 
fertility of the offspring. The same end is gained by 
dichogamy or the maturation of the reproductive ele- 
‘ments of the same flower at different periods,—by 
diceciousness—self-sterility—the prepotency of pollen 
from another individual over a plant’s own pollen,—and 
lastly, by the structure of the flower in relation to the 
visits of insects. The wonderful diversity of the means 
for gaining the same end in this case, and in many 
others, depends on the nature of all the previous 
changes through which the species has passed, and on 
the more or less complete inheritance of the successive 
adaptations of each part to the surrounding conditions. 


Ouapr. VI. ON HETEROSTYLED PLANTS. 259 


Plants which are already well adapted by the structure 
of their flowers for cross-fertilisation by the aid of 
insects often possess an irregular corolla, which has 
been modelled in relation to their visits; and it would 
have been of little or no use to such plants to have 
become heterostyled. We can thus understand why 
it is that not a single species is heterostyled in such 
great families as the Leguminose, Labiate, Scrophu- 
lariaceee, Orchidew, &c., all of which have irregular 
flowers. Every known heterostyled plant, however, 
depends on insects for its fertilisation, and not on the 
wind ; so that it is a rather surprising fact that only 
one genus, Pontederia, has a plainly irregular corolla. 

Why some species are adapted for cross-fertilisation, 
whilst others within the same genus are not so, or 
if they once were, have since lost such adaptation 
and in consequence are now usually self-fertilised, I 
have endeavoured elsewhere to explain to a certain 
limited extent.* If it be further asked why some 
species have been adapted for this end by being made 
heterostyled, rather than by any of the above specified 
means, the answer probably lies in the manner in 
which heterostylism originated,—a subject immedi- 
ately to be discussed. Heterostyled species, however, 
have an advantage over dichogamous species, as all 
the flowers on the same heterostyled plant belong to 
the same form, so that when fertilised legitimately by 
insects two distinct individuals are sure to intercross. 
On the other hand, with dichogamous plants, early or 
late flowers on the same individual may intercross ; 
and a cross of this kind does hardly any or no good. 
Whenever it is profitable to a species to produce a 


* ‘The Effects of Cross and Self-fertilisation,’ 1876, p. 441. 


260 CONCLUDING REMARKS Cuar. VI 


large number of seeds and this obviously is a very 
common case, heterostyled will have an advantage 
over dicecious plants, as all the individuals of the 
former, whilst only half of the latter, that is the 
females, yield seeds. On the other hand, hetero- 
styled plants seem to have no advantage, as far as 
cross-fertilisation is concerned, over those which are 
sterile with their own pollen. They le indeed under 
a slight disadvantage, for if two self-sterile plants 
grow near together and far removed from all other 
plants of the same species, they will mutually and 
perfectly fertilise one another, whilst this will not be 
the case with heterostyled dimorphic plants, unless 
they chance to belong to opposite forms. 

It may be added that species which are trimorphic 
have one slight advantage over the dimorphic; for if 
only two individuals of a dimorphic species happen 
to grow near together in an isolated spot, the chances 
are even that both will belong to the same form, and 
in this case they will not produce the full number of 
vigorous and fertile seedlings; all these, moreover, 
will tend strongly to belong to the same form as their 
parents. On the other hand, if two plants of the same 
trimorphic species happen to grow in an isolated spot, 
the chances are two to one in favour of their not be- 
longing to the same form; and in this case they will 
legitimately fertilise one another, and yield the full 
complement of vigorous offspring. 


The Means by which Plants may have been rendered 
Heterostyled. 


This is a very obscure subject, on which I can throw 
little light, but which is worthy of discussion. It has 


Cuar. VI. ON HETEROSTYLED PLANTS. 261 


been shown that heterostyled plants occur in fourteen 
natural families, dispersed throughout the whole vege- 
table kingdom, and that even within the family of the 
Rubiacez they are dispersed in eight of the tribes. We 
may therefore conclude that this structure has been 
acquired by various plants independently of inheritance 
from a common progenitor, and that it can be acquired 
without any great difficulty—that is, without any very 
unusual combination of circumstances. 

It is probable that the first step towards a species 
becoming heterostyled is great variability in the length 
of the pistil and stamens, or of the pistil alone. Such 
variations are not very rare: with Amsinckia spectabilis 
and Nolana prostrata these organs differ so much in 
length in different individuals that, until experiment- 
ing on them, I thought both species heterostyled. 
The stigma of Gesneria pendulina sometimes protrudes 
far beyond, and is sometimes seated beneath the 
anthers; so it is with Ovzalis acetosella and various 
other plants. I have also noticed an extraordinary 
amount of difference in the length of the pistil in cul- 
tivated varieties of Primula veris and vulgaris. 

As most plants are at least occasionally cross-fer- 
tilised by the aid of insects, we may assume that this 
was the case with our supposed varying plant; but 
that it would have been beneficial to it to have been 
more regularly cross-fertilised. We should bear in 
mind how important an advantage it has been 
proved to be to many plants, though in different 
degrees and ways, to be cross-fertilised. It migh~ 
well happen that our supposed species did not vary 
in function in the right manner, so as to become 
either dichogamous or completely self-sterile, or in 
structure so as to ensure cross-fertilisation. If it had 


262 CONCLUDING REMARKS Cuap. VI. 


thus varied, it would never haye been rendered hetero- 
styled, as this state would then have been superfluous. 
But the parent-species of our several existing hetero- 
styled plants may haye been, and probably were (judg- 
ing from their present constitution) in some degree 
self-sterile ; and this would have made regular cross- ~ 
fertilisation still more desirable. 

Now let us take a highly varying species with most 
or all of the anthers exserted in some individuals, and 
in others seated low down in the corolla; with the 
stigma also varying in position in like manner. Insects 
which visited such flowers would have different parts 
of their bodies dusted with pollen, and it would be a 
mere chance whether this were left on the stigma of 
the next flower which was visited. If all the anthers 
could have been placed on the same level in all the 
plants, then abundant pollen would have adhered to 
the same part of the body of the insects which fre- 
quented the flowers, and would afterwards have been 
deposited without loss on the stigma, if it likewise 
stood on the same unvarying level in all the flowers. 
But as the stamens and pistils are supposed to have 
already varied much in length and to be still varying, 
it might well happen that they could be reduced much 
more easily through natural selection into two sets of 
different lengths in different individuals, than all to 
the same length and level in all the individuals. We 
know from innumerable instances, in which the two 
sexes and the young of the same species differ, that 
there is no difficulty in two or more sets of individuals 
being formed which inherit different characters. In 
our particular case the law of compensation or balance- 
ment (which is admitted by many botanists) would 
tend to cause the pistil to be reduced in those indi- 


Cuar. VL. ON HETEROSTYLED PLANTS. 263 


viduals in which the stamens were greatly developed, 
and to be increased in length in those which had their 
stamens but little developed. 

Now if in our varying species the longer stamens 
were to be nearly equalised in length in a considerable 
body of individuals, with the pistil more or less reduced ; 
and in another body, the shorter stamens to be simi- 
larly equalised, with the pistil more or less increased in 
length, cross-fertilisation would be secured with little 
loss of pollen; and this change would be so highly 
beneficial to the species, that there is no difficulty in be- 
lieying that it could be effected through natural selec- 
tion. Our plant would then make a close approach in 
structure to a heterostyled dimorphic species ; or to a 
trimorphic species, if the stamens were reduced to two 
lengths in the same flower in correspondence with that 
of the pistils in the other two forms. But we have not 
as yet even touched on the chief difficulty in under- 
standing how heterostyled species could have origi- 
nated. A completely self-sterile plant or a dicho- 
gamous one can fertilise and be fertilised by any 
other individual of the same species; whereas the 
essential character of a heterostyled plant is that an 
individual of one form cannot fully fertilise or be fer- 
tilised by an individual of the same form, but only 
by one belonging to another form. 

H. Miller has suggested* that ordinary or homo- 
styled plants may have been rendered heterostyled 
merely through the effects of habit. Whenever pollen 
from one set of anthers is habitually applied to a pistil 
of particular length in a varying species, he believes 
that at last the possibility of fertilisation in any other 


* ‘Die Befruchtung der Blumen,’ p. 352. 


264 CONCLUDING REMARKS Cuap. VI. 


manner will be nearly or completely lost. He was 
led to this view by observing that Diptera frequently 
carried pollen from the long-styled flowers of Hottonia 
to the stigma of the same form, and that this ille- 
gitimate union was not nearly so sterile as the corre- 
sponding union in other heterostyled species. But 
this conclusion is directly opposed by some other 
cases, for instance by that of Linwm grandiflorum ; 
for here the long-styled form is utterly barren with 
its own-form pollen, although from the position 
of the anthers this pollen is invariably applied to 
the stigma. It is obvious that with heterostyled 
dimorphic plants the two female and the two male 
organs differ in power; for if the same kind of pollen 
be placed on the stigmas of the two forms, and again 
if the two kinds of pollen be placed on the stigmas of 
the same form, the results are m each case widely dif- 
ferent. Nor can we see how this differentiation of the 
two female and two male organs could have been 
effected merely through each kind of pollen being 
habitually placed on one of the two stigmas. 

Another view seems at first sight probable, namely, 
that an incapacity to be fertilised in certain ways has 
been specially acquired by heterostyled plants. We 
may suppose that our varying species was somewhat 
sterile (as is often the case) with pollen from its own 
stamens, whether these were long or short; and that 
such sterility was transferred to all the individuals 
with pistils and stamens of the same length, so that 
these became incapable of intercrossing freely ; but 
that such sterility was eliminated in the case of the 
individuals which differed in the length of their pistils 
and stamens. It is, however, incredible that so peculiar 
a form of mutual infertility should have been specially 


Cnap. VI. ON HETEROSTYLED PLANTS. 265 


acquired unless it were highly beneficial to the species ; 
and although it may be beneficial to an individual 


‘plant to be sterile with its own pollen, cross-fertilisa- 


tion being thus ensured, how can it be any advan- 
tage to a plant to be sterile with half its brethren, 
that is, with all the individuals belonging to the 
same form? Moreover, if the sterility of the unions 
between plants of the same form had been a special 
acquirement, we might have expected that the long- 
styled form fertilised by the long-styled would have 
been sterile in the same degree as the short-styled 
fertilised by the short-styled; but this is hardly ever 
the case. On the contrary, there is sometimes the 
widest difference in this respect, as between the two 
illegitimate unions of Pulmonaria angustifolia and of 
Hottonia palustris. 

It is a more probable view that the male and female 
organs in two sets of individuals have been by some 
means specially adapted for reciprocal action; and 
that the sterility between the individuals of the same 
set or form is an incidental and purposeless result. 
The meaning of the term “incidental” may be illus- 
trated by the greater or less difficulty in grafting or 
budding together two plants belonging to distinct 
species ; for as this capacity is quite immaterial to the 
welfare of either, it cannot have been specially ac- 
quired, and must be the incidental result- of differ- 
ences in their vegetative systems. But how the 
sexual elements of heterostyled plants came to differ 
from what they were whilst the species was homo- 
styled, and how they became co-adapted in two sets of 
individuals, are very obscure points. We know that 
in the two forms of our existing heterostyled plants 
the pistil always differs, and the stamens generally 
differ in length; so does the stigma in structure, 


266 CONCLUDING REMARKS Cuap. VI. 


the anthers in size, and the pollen-grains in diameter. 
It appears, therefore, at first sight probable that 
organs which differ in such important respects could ° 
act on one another only in some manner for which 
they had been specially adapted. The probability of 
this view is supported by the curious rule that the 
greater the difference in length between the pistils 
and stamens of the trimorphiec species of Lythrum and 
Oxalis, the products of which are united for reproduc- 
tion, by so much the greater is the infertility of the 
union. ‘The same rule applies to the two illegitimate 
unions of some dimorphic species, namely, Primula 
vulgaris and Pulmonaria angustifolia ; but it entirely 
fails in other cases, as with Hottonia palustris and 
Linum grandiflorum. We shall, however, best perceive 
the difficulty of understanding the nature and origin 
of the co-adaptation between the reproductive organs 
of the two forms of heterostyled plants, by consider- 
ing the case of Linum grandiflorum: the two forms of 
this plant differ exclusively, as far as we can see, in 
the length of their pistils; in the long-styled form, 
the stamens equal the pistil in length, but their 
pollen has no more effect on it than so much in- 
organic dust; whilst this pollen fully fertilises the 
short pistil of the other form. Now, it is scarcely 
credible that a mere difference in the length of the © 
pistil can make a wide difference in its capacity for 
being fertilised. We can believe this the less because 
with some plants, for instance, Amsinckia spectabilis, 
the pistil varies greatly in length without affecting 
the fertility of the individuals which are intercrossed. 
So again I observed that the same plants of Primula 
veris and vulgaris differed to an extraordinary degree 
in the length of their pistils during successive seasons ; 
nevertheless they yielded during these seasons exactly 


Cuar. VI. ON HETEROSTYLED PLANTS. 267 


the same average number of seeds when left to fertilise 
themselves spontaneously under a net. 

We must therefore look to the appearance of inner 
or hidden constitutional differences between the indi- 
viduals of a varying species, of such a nature that the 
male element of one set is enabled to act efficiently 
only on the female element of another set. We need 
not doubt about the possibility of variations in the 
constitution of the reproductive system of a plant, for 
we know that some species vary so as to be completely 
self-sterile or completely self-fertile, either in an appa- 
rently spontaneous manner or from slightly changed 
conditions of life. Gartner also has shown* that the in- 
dividual plants of the same species vary in their sexual 
powers in such a manner that one will unite with a 
distinct species much more readily than another. But 
what the nature of the inner constitutional differences 
may be between the sets or forms of the same varying 
species, or between distinct species, is quite unknown. 
It seems therefore probable that the species which 
have become heterostyled at first varied so that two 
or three sets of individuals were formed differing in 
the length of their pistils and stamens and in other 
co-adapted characters, and that almost simultaneously 
their reproductive powers became modified in such a 
manner that the sexual elements in one set were 
adapted to act on the sexual elements of another set ; 
and consequently that these elements in the same set 
or form incidentally became ill-adapted for mutual 
interaction, as in the case of distinct species. I have 
elsewhere shownf that the sterility of species when 


* Gartner, ‘ Bastarderzeugung Plants under Domestication,’ 2nd 
im Pflanzenreich,’ 1849, p. 165. edit. vol. ii. p. 169; ‘ The Effects of 
t ‘Origin of Species,’ 6th edit. | Cross and Self-fertilisation,’ p.463. 
p- 247; ‘ Variation of Animalsanud It may be well here to remark 


268 CONCLUDING REMARKS Cuapr. VI. 


first crossed and of their hybrid offspring must also 
be looked at as merely an incidental result, following 
from the special co-adaptation of the sexual elements 
of the same species. We can thus understand the 
striking parallelism, which has been shown to exist 
between the effects of illegitimately uniting hetero- 
styled plants and of crossing distinct species. The 
great difference in the degree of sterility between the 
various heterostyled species when illegitimately fer- 
tilised, and between the two forms of the same species 
when similarly fertilised, harmonises well with the 
view that the result is an incidental one which follows 
from changes gradually effected in their reproductive 
systems, in order that the sexual elements of the dis- 
tinct forms should act perfectly on one another. 


Transmission of the Two Forms by Heterostyled Plants. . 
—The transmission of the two forms by heterostyled 
plants, with respect to which many facts were given in 
the last chapter, may perhaps be found hereafter to 
throw some light on their manner of development. 
Hildebrand observed that seedlings from the long- 
styled form of Primula Sinensis when fertilised with 
pollen from the same form were mostly long-styled, 
and many analogous cases have since been observed 
by me. All the known cases are given in the two 
following tables. 


that, judging from the remark- 
able power with which abruptly 
changed conditions of life act on 
the reproductive system of most 
organisms, it is probable that the 
close adaptation of the male to the 


female elements in the two forms of 
the same heterostyled species, or 
in all the individuals of the same 
ordinary species, could be acquired 
only under long-continued nearly 
uniform conditions of life. 


~ . i, 


Ciar. VI. ON HETEROSTYLED PLANTS. 269 
TABLE 36. 
Nature of the Offspring from Illegitimately fertilised Dimor phic 
Plants. 


Number | Numb:-r 
of Long- | of Short- 

L styled | styled 

| ffspring.|Offspring. 


own-form pollen during five 156 6 


successive generations, _— 


Long-styled form, fertilised by 
Primula veris | 


duced. . 
own-form pollen, produced 


| 
Short-styled form, fertilised Py} 5 9 
| 


own-form pollen during two 
successive ee ag 
duced, : 


69 0 


Primula vulgaris 


hort-styled form, fertilised by 
own-form pollen, is said to 
Primula auricula .4 produce during successive 
} generations offspring in about 
| the following proportions 


bs ng-styled form, fertilised 4 
(s 
| 


25 75 


own-torm pollen during two 
successive te BS 
duced sei". 


Primula Sinensis . 


‘| 
Long-styled form, fertilised by 
| sa | 0 


14 3 


A pe ate form, fertilised by 
own-form pollen ee 


brand), produced. . 


gee form, fertilised by 24 


own-form pollen, produced . 


ry 


Long-styled form, fertilised by 


own-form pollen, produced . = 2 


Pulmonaria officinalis 


prepepeas ey yram own-form pollen, produced 


Short-styled form, fertilised by 


own-form pollen, produced 


bss ap oa form, fertilised by 4) 45 4 
{ } i3 | 20 


270 


TABLE 37. 


Nature of the Offspring from Illegitimately 
Plants. 


Long-styled form, fertilised 
by own-form Bee DFS. 


Lythrum salicaria. 
duced . 


| 


“a 


\ 


De rigaie ty form, fertilised 
by own-form gia ee 
duced . 


Short-styled form, fertilised 
by pollen from mid-length 
stamens of long -styled 
form, produced 


Mid-styled form, fertilised by 


v4 own-form pollen, produced 


pollen from shortest sta- 

mens of behauic eds aes 

produced . 

Mid-styled form, fertilised by 
pollen from longest sta- 
mens of shor ae oe 
produced 


Long-styled form, fertilised 
during several generations 
by own-form pollen, pro- 
duced 
ratio of 


Oxalis rosea 


Sees in the 


ie form, fertilised by 
( 


Mid-styled form, fertilised by 
wn-form pollen, produced 


“3 hedysaroides) 


1 


CONCLUDING REMARKS 


Cuap. VI. 


fertilised Trimorphic 


| 
Number | Number 
of Mid- | of Short- 
styled styled 


Number 
of Long- 
styled 


Offspring. Offspring. tebe ss 


56 0 0 
1 0 8 

+ 0 8 

1 3 0 
aw 8 0 
14 8 18 

| 

100 0 0 
0 17 C 


Cuar. VI. ON HETEROSTYLED PLANTS. 271 


We see in these two tables that the offspring from 
a form illegitimately fertilised with pollen from 
another plant of the same form belong, with a few 
exceptions, to the same form as their parents. For 
instance, out of 162 seedlings from long-styled plants 
of Primula veris fertilised during five generations in 
this manner, 156 were long-styled and only 6 short- 
styled. Of 69 seedlings from P. vulgaris similarly 
raised all were long-styled. So it was with 56 seedlings 
from the long-styled form of the trimorpnic Lythrum 
salicaria, and with numerous seedlings from the long- 
styled form of Oxalis rosea. The offspring from the 
short-styled forms of dimorphic plants, and from both 
the mid-styled and short-styled forms of trimorphic 
plants, fertilised with their own-form pollen, likewise 
tend to belong to the same form as their parents, but 
not in so marked a manner as in the ease of the long- 
styled form. There are three cases in Table 37, in 
which a form of Lythrum was fertilised illegitimately 
with pollen from another form; and in two of these 
ceases all the offspring belonged to the same two forms 
as their parents, whilst in the third case they belonged 
to all three forms. 

The cases hitherto given relate to illegitimate unions, 
but Hildebrand, Fritz Miller, and myself found that 
a very large proportion, or all of the offspring, from a 
legitimate union between any two forms of the tri- 
morphic species of Oxalis belonged to the same two 
forms. A similar rule therefore holds good with unions 
which are fully fertile, as with those of an illegiti- 
mate nature which are more or less-sterile. When 
some of the seedlings from a heterostyled plant belong 
to a different form from that of its parents, Hildebrand 
accounts for the fact by reversion. For instance, the 
long-styled parent-plant of Primula veris, from which 


ie CONCLUDING REMARKS Cuar. VI. 


the 162 illegitimate seedlings in Table 36 were derived 
in the course of five generations, was itself no doubt 
derived from the union of a long-styled and a short- 
styled parent ; and the 6 short-styled seedlings may be 
attributed to reversion to their short-styled progeni- 
tor. But it is a surprising fact in this case, and im 
other similar ones, that the number of the offspring 
which thus reverted was not larger. The fact is ren- 
dered still more strange in the particular instance of 
P. veris, for there was no reversion until four or five 
generations of long-styled plants had been raised. It 
may be seen in both tables that the long-styled form 
transmits its form much more faithfully than does the 
short-styled, when both are fertilised with their own- 
form pollen; and why this should be so it is difficult 
to conjecture, unless it be that the aboriginal parent- 
form of most heterostyled species possessed a pistil 
which exceeded its own stamens considerably in 
length.* I will only add that in a state of nature 
any single plant of a trimorphic species no doubt pro- 
duces all three forms; and this may be accounted for 
either by its several flowers being separately fertilised 
by both the other forms, as Hildebrand supposes; or 
by pollen from both the other forms being deposited 
by insects on the stigma of the same flower. 
Equal-styled varieties—The tendency of the di- 
morphie species of Primula to produce equal-styled 
varieties deserves notice. Cases of this kind have 


* It may be suspected that this 
was the case with Primula, judg- 


state of nature with some flowers 
on the same plant long-styled, 


ing from the length of the pistil 
in several allied genera (see 
Mr. J. Scott, ‘Journal Linn. Soe. 
Bot.’ vol. viii. 1864, p. 85). Herr 
Breitenbach found many specimens 
of Primula elatior growing in a 


others short-styled and _ others 
equal-styled ; and the long-styled 
form greatly preponderated in 
number; there being 61 of this 
form to 9 of the short-styled and 
15 of the equal-styled. 


Crap. VI. ON HETEROSTYLED PLANTS. 273 


been observed, as shown in the last chapter, in no less 
than six species, namely, P. veris, vulgaris, Sinensis, 
auricula, farinosa, and elatior. In the case of P. veris, 
the stamens resemble in length, position and size 
of their pollen-grains the stamens of the short-styled 
form; whilst the pistil closely resembles that'of the 
long-styled, but as it varies much in length, one proper 
to the short-styled form appears to have been elongated 
and to have assumed at the same time the functions 
of a long-styled pistil. Consequently the flowers are 
capable of spontaneous self-fertilisation of a legiti- 
mate nature and yield a full complement of seed, or 
even more than the number produced by ordinary 
flowers legitimately fertilised. With P. Sinensis, on 
the other hand, the stamens resemble in all respects 
the shorter ones proper to the long-styled form, whilst 
the pistil makes a near approach to that of the short- 
styled, but as it varies in length, it would appear as 
if a long-styled pistil had been reduced in length and 
modified in function. The flowers in this case as in 
the last are capable of spontaneous legitimate ferti- 
lisation, and are rather more productive than ordinary 
flowers legitimately fertilised. With P. auricula and 
farinosa the stamens resemble those of the short-styled 
form in length, but those of the long-styled in the 
size of their pollen-grains ; the pistil also resembles that 
of the long-styled, so that although the stamens and 
pistil are of nearly equal length, and consequently 
pollen is spontaneously deposited on the stigma, yet 
the flowers are not legitimately fertilised and yield 
only a very moderate supply of seed. We thus see, 
firstly, that equal-styled varieties have originated in 
various ways, and, secondly, that the combination of 
the two forms in the same flower differs in complete- 


274 CONCLUDING REMARKS Cuap. VI. 


ness. With P. elatior some of the flowers on the same 
plant have become equal-styled, instead of all of 
them as in the other species. 

Mr. Scott has suggested that the equal-styled varie- 
ties arise through reversion to the former homostyled 
condition of the genus. This view is supported by 
the remarkable fidelity with which the equal-styled 
variation is transmitted after it has once appeared. I 
have shown in Chapter XIII. of my ‘ Variation of 
Animals and Plants under Domestication,’ that any 
cause which disturbs the constitution tends to in- 
duce reversion, and it is chiefly the cultivated 
species of Primula which become equal-styled. Ile- 
gitimate fertilisation, which is an abnormal process, 
is likewise an exciting cause; and with illegitimately 
descended long-styled plants of P. Sinensis, I have 
observed. the first appearance and subsequent stages 
of this variation. With some other plants of P. Si- 
nensis of similar parentage the flowers appeared 
to haye reverted to their original wild condition. 
Again, some hybrids between P. veris and vulgaris 
were strictly equal-styled, and others made a near 
approach to this structure. AIl these facts support 
the view that this variation results, at least in part, 
from reversion to the original state of the genus, 
before the species had become heterostyled. On the 
other hand, some considerations indicate, as previously 
remarked, that the aboriginal parent-form of Primula 
had a pistil which exceeded the stamens in length. 
The fertility of the equal-styled varieties has been 
somewhat modified, being sometimes greater and some- 
times less than that of a legitimate union. Another 
view, however, may be taken with respect to the origin 
of the equal-styled varieties, and their appearance 
may be compared with that of hermaphrodites amongst . 


Cuar. VI. ON HETEROSTYLED PLANTS. x Ba 


animals which properly have their sexes separated ; 
for the two sexes are combined in a monstrous her- 
maphrodite in a somewhat similar manner as the 
two sexual forms are combined in the same flower of 
an equal-styled variety of a heterostyled species. 


Final remarks.—The existence of plants which have 
been rendered heterostyled is a highly remarkable 
phenomenon, as the two or three forms of the same 
undoubted species differ not only in important points 
of structure, but in the nature of their reproductive 
powers. As far as structure is concerned, the two 
sexes of many animals and of some plants differ to an 
extreme degree; and in both kingdoms the same 
species may consist of males, females, and hermaphro- 
dites. Certain hermaphrodite cirripedes are aided in 
their reproduction by a whole cluster of what I have 
called complemental males, which differ wonderfully 
from the ordinary hermaphrodite form. With ants 
we have males and females, and two or three castes of 
sterile females or workers. With Termites there are, 
as Fritz Miller has shown, both winged and wingless 
males and females, besides the workers. But in none 
of these cases is there any reason to believe that the 
several males or several females of the same species 
differ in their sexual powers, except in the atrophied 
condition of the reproductive organs in the workers of 
social insects. Many hermaphrodite animals must 
unite for reproduction, but the necessity of such 
union apparently depends solely on their structure. 
On the other hand, with heterostyled dimorphic 
species there are two females and two sets of males, 
and with trimorphiec species three females and three 
sets of males, which differ essentially in their sexual 


aie = CONCLUDING REMARKS Cuap. VI, 


powers. We shall, perhaps, best perceive the complex 
and extraordinary nature of the marriage arrangements 
of a trimorphic plant by the following illustration. 
Let us suppose that the individuals of the same species 
of ant always lived in triple communities; and that 
in one of these, a large-sized female (differing also in 
other characters) lived with six middle-sized and six 
small-sized males ; in the second community a middle- 
sized female lived with six Jarge- and six small-sized 
males; and in the third, a small-sized female lived 
with six large- and six middle-sized males. Each of 
these three females, though enabled to unite with any 
male, would be nearly sterile with her own two sets of 
males, and likewise with two other sets of males of the 
same size with her own which lived in the other two 
communities ; but she would be fully fertile when 
paired with a male of her own size. Hence the thirty- 
six males, distributed by half-dozens in the three com- 
munities, would be divided into three sets of a dozen 
each; and these sets, as well as the three females, 
would differ from one another in their reproductive 
powers in exactly the same manner as do the distinct 
species of the same genus. But it is a still more 
remarkable fact that young ants raised from any one 
of the three female ants, illegitimately fertilised by a 
male of a different size would resemble in a whole 
series of relations the hybrid offspring from a cross 
between two distinct species of ants. They would be 
dwarfed in stature, and more or less, or even utterly 
barren. Naturalists are so much accustomed to behold 
great diversities of structure associated with the two 
sexes, that they feel no surprise at almost any amount, 
of difference ; but differences in sexual nature have 
been thought to be the very touchstone of specific 
distinction. We now see that such sexual differences 


Cuapr. VI. ON HETEROSTYLED PLANTS. 277 


—the greater or less power of fertilising and being 
fertilised—may characterise the co-existing individuals 
of the same species, in the same manner as they 
characterise and have kept separate those groups of 
individuals, produced during the lapse of ages, which 
we rank and denominate as distinct species. 


278 DIHCIOUS AND Cuar. VIL 


CHAPTER VII. 
Potycamous, Dicaectous, AND GyNo-Di@crous PLANTS. 


The conversion in various ways of hermaphrodite into dicecious plants 
—Heterostyled plants rendered dicecious—Rubiaceze—Verbenacese 
—Polygamous and sub-dicecious plants—Euonymus—Fragaria— 
The two sub-forms of both sexes of Rhamnus and Epigseea—Ilex— 
Gyno-dicecious plants—Thymus, difference in fertility of the her- 
maphrodite and female individuals—Satureia—Manner in which 
the two forms probably originated—Scabiosa and other gyno- 
dicecious plants—Difference in the size of the corolla in the forms 
of polygamous, dicecious, and gyno-dicecious plants, 


THERE are several groups of plants in which all the 
species are dicecious, and these exhibit no rudiments 
in the one sex of the organs proper to the other. 
About the origin of such plants nothing is known. It 
is possible that they may be descended from ancient 
lowly organised forms, which had from the first their 
sexes separated ; so that they have never existed as 
hermaphrodites. There are, however, many other 
groups of species and single ones, which from being 
allied on all sides to hermaphrodites, and from ex- 
hibiting in the female flowers plain rudiments of 
male organs, and conversely in the male flowers rudi- 
ments of female organs, we may feel sure are descended 
from plants which formerly had the two sexes com- 
bined in the same flower. It is a curious and obscure 
problem how and why such hermaphrodites have been 
rendered bisexual. 

If in some individuals of a species the stamens 
alone were to abort, females and hermaphrodites would 


Cuapr. VII. POLYGAMOUS PLANTS. 279 


be left existing, of which many instances occur; and 
if the female organs of the hermaphrodite were after- 
wards to abort, the result would be a dicecious plant. 
Conversely, if we imagine the female organs alone to 
abort in some individuals, males and hermaphrodites 
would be left; and the hermaphrodites might after- 
wards be converted into females. 

In other cases, as in that of the common Ash-tree 
mentioned in the Introduction, the stamens are rudi- 
mentary in some individuals, the pistils in others, 
others again remaining as hermaphrodites. Here the 
modification of the two sets of organs appears to have 
occurred simultaneously, as far as we can judge from 
their equal state of abortion. If the hermaphrodites 
were supplanted by the individuals having separated 
sexes, and if these latter were equalised in number, a 
strictly dicecious species would be formed. 

There is much difficulty in understanding why her- 
maphrodite plants should ever have been rendered 
dicecious. There would be no such conversion, unless 
pollen was already carried regularly by insects or by the 
wind from one individual to the other; for otherwise 
every step towards diceciousness would lead towards 
sterility. As we must assume that cross-fertilisation 
was assured before an hermaphrodite could be changed 
into a dicecious plant, we may conclude that the con- 
version has not been effected for the sake of gaining 
the great benefits which follow from cross-fertilisa- 
tion. We can, however, see that if a species were 
subjected to unfavourable conditions from severe com- 
petition with other plants, or from any other cause, the 
production of the male and female elements and the 
maturation of the ovules by the same individual, might 
prove too great a strain on its powers, and the separa- 
tion of the sexes would then be highly beneficial. 

13 


280 DIGHCIOUS AND Cuar. VII. 


This, however, would be effected only under the con- 
tingency of a reduced number of seeds, produced by 
the females alone, being sufficient to keep up the 
stock. ft 

There is another way of looking at the subject which 
partially removes a difficulty that appears at first sight 
insuperable, namely, that during the conversion of an 
hermaphrodite into a dicecious plant, the male organs 
must abort in some individuals and the female organs 
in others. Yet as all are exposed to the same con- 
ditions, it might have been expected that those 
which varied would tend to vary in the same man- 
ner. As a general rule only a few individuals of a 
species vary simultaneously in the same manner; and 
there is no improbability in the assumption that 
some few individuals might produce larger seeds 
than the average, better stocked with nourishment. If 
the production of such seeds were highly beneficial to 
a species, and on this head there can be little doubt,* 
the variety with the large seeds would tend to in- 
crease. But in accordance with the law of compensa- 
tion we might expect that the individuals which pro- 
duced such seeds would, if living under severe con- 
ditions, tend to produce less and less pollen, so that 
their anthers would be reduced in size and might ulti- 
mately become rudimentary. This view occurred to 
me owing to a statement by Sir J. E. Smithf that 
there are female and hermaphrodite plants of Serratula 
tinctoria, and that. the seeds of the former are larger 
than those of the hermaphrodite form. It may also 
be worth while to recall the case of the mid-styled 
form of Lythrum salicaria, which produces a larger 


* See the facts given in ‘The t ‘Trans. Linn. Soc., vol. xiii. 
Effects of Cross and Self-fertilisa- —__p. 600. 
tion, p. 353. 


wd 


Cuae. VIL. POLYGAMOUS PLANTS. 281 


number of seeds than the other forms, and has some- 
what smaller pollen-grains which have less fertilising 
power than those of the corresponding stamens in the 
other two forms; but whether the larger number of 
seeds is the indirect cause of the diminished power 
of the pollen, or vice versé, I know not. As soon 
as the anthers in a certain number of individuals be- 
came reduced in size in the manner just suggested or 


_ from any other cause, the other individuals would have 


to produce a larger supply of pollen; and such in- 
creased development would tend to reduce the female 
organs through the law of compensation, so as ulti- 
mately to leave them in a rudimentary condition ; 
and the species would then become dicecious. 

Instead of the first change occurring in the female 
organs we may suppose that the male ones first varied, 
so that some individuals produced a larger supply of 
pollen. This would be beneficial under certain cir- 
cumstances, such as a change in the nature of the 
insects which visited the flowers, or in their be- 
coming more anemophilous, for such plants require an 
enormous quantity of pollen. The increased action of 
the male organs would tend to affect through compen- 
sation the female organs of the same flower; and the 
final result would be that the species would consist of 
males and hermaphrodites. But it is of no use con- 
sidering this case and other analogous ones, for, as 
stated in the Introduction, the co-existence of male 
and hermaphrodite plants is excessively rare. 

It is no valid objection to the foregoing views that 
changes of such a nature would be effected with ex- 
treme slowness, for we shall presently see good reason 
to believe that various hermaphrodite plants have 
become or are becoming dicecious by many and ex- 
cessively small steps. In the case of polygamous 


282 DIGCIOUS AND Cuap. VII. 


species, which exist as males, females and hermaphro- 
dites, the latter would have to be supplanted before 
the species could become strictly dicecious ; but the 
extinction of the hermaphrodite form would probably 
not be difficult, as a complete separation of the sexes 
appears often to be in some way beneficial. The males 
and females would also have to be equalised in 
number, or produced in some fitting proportion for the 
effectual fertilisation of the females. 

There are, no doubt, many unknown laws which 
govern the suppression of the male or female organs 
in hermaphrodite plants, quite independently of any 
tendency in them to become moncecious, dicecious, or 
polygamous. We see this in those hermaphrodites 
which from the rudiments still present manifestly 
once possessed more stamens or pistils than they 
now do,—even twice as many, as a whole verticil has 
often been suppressed. Robert Brown remarks* that 
“the order of reduction or abortion of the stamina 
in any natural family may with some confidence be 
predicted,” by observing in other members of the 
family, in which their number is complete, the order 
of the dehiscence of the anthers; for the lesser per- 
manence of an organ is generally connected with its 
lesser perfection, and he judges of perfection by 
priority of development. He also states that when- 
ever there is a.separation of the sexes in an her- 
maphrodite plant, which bears flowers on a simple 
spike, it is the females which expand first; and this 
he likewise attributes to the female sex being the 
more perfect of the two, but why the female should 
be thus valued he does not explain. 


* «Trans. Linn. Soe,’ vol, xii. p. 98. Or ‘ Miscellaneous Works,’ vol. 
ii. pp. 278-81. 


Cuar. VII. POLYGAMOUS PLANTS. 283 


Plants under cultivation or changed conditions of 
life frequently become sterile; and the male organs 
are much oftener affected than the female, though the 
latter alone are sometimes affected. The sterility of 
the stamens is generally accompanied by a reduction 
in their size ; and we may feel sure, from a wide-spread 
analogy, that both the male and female organs would 
become rudimentary in the course of many genera- 
tions if they failed altogether to perform their proper 
functions. According to Girtner,* if the anthers on 
a plant are contabescent (and when this occurs it is 
always at a very early period of growth) the female 
organs are sometimes precociously developed. I 
mention this case as it appears to be one of com- 
pensation. So again is the well-known fact, that 
plants which increase largely by stolons or other such 
means are often utterly barren, with a large proportion 
of their pollen-grains in a worthless condition. 

Hildebrand has shown that with hermaphrodite 
plants which are strongly proterandrous, the stamens 
in the flowers which open first sometimes abort; and 
this seems to foliow from their being useless, as no 
pistils are then ready to be fertilised. Conversely 
the pistils in the flowers which open last sometimes 
abort; as when they are ready for fertilisation all the 
pollen has been shed. He further shows by means of 
a series of gradations amongst the Composite, t that 
a tendency from the causes just specified to produce 
either male or female florets, sometimes spreads 
to all the florets on the same head, and sometimes 


* ‘Beitriige zur Kenntniss, &e. chap. xviii—2nd edit. vol. ii. 
p- 117 et seq. Thewhole subject pp. 146-56. 
of the sterility of plants from + ‘Ueber die Geschlechtsver- 
various causes has been discussed hialtnisse bei den Compositen,’ 
in my ‘Variation of Animals 1869, p. 89. 
and Plants under Domestication,’ 


284 DIGCIOUS AND Cuap. VII. 


even to the whole plant; and in this latter case the 
species becomes dicecious. In those rare instances men- 
tioned in the Introduction, in which some of the indi- 
viduals of both moncecious and hermaphrodite plants 
are proterandrous, others being proterogynous, their 
conversion into a dicecious condition would probably be 
much facilitated, as they already consist of two bodies 
of individuals, differing to a certain extent in their 
reproductive functions. 

Dimorphic heterostyled plants offer still more 
strongly marked facilities for becoming dicecious; for 
they likewise consist of two bodies of individuals in 
upproximately equal numbers, and what probably is 
more important, both the male and female organs 
differ in the two forms, not only in structure but in 
function, in nearly the same manner as do the repro- 
ductive organs of two distinct species belonging to 
the same genus. Now if two species are subjected to 
changed conditions, though of the same nature, it is 
notorious that they are often affected very differently ; 
therefore the male organs, for instance, in one form of 
a heterostyled plant might be affected by those un- 
known causes which induce abortion, differently from 
the homologous but functionally different organs in 
the other form; and so conversely with the female 
organs. Thus the great difficulty before alluded to is 
much lessened in understanding how any cause what- 
ever could lead to the simultaneous reduction and 
ultimate suppression of the male organs in half the 
individuals of a species, and of the female organs in 
the other half, whilst all were subjected to exactly the 
same conditions of life. 

That such reduction or suppression has occurred 
in some heterostyled plants is almost certain. The 
Rubiacez contain more heterostyled genera than any 


Cuap. VII POLYGAMOUS PLANTS. 285 


other family, and from their wide distribution we may 
infer that many of them became heterostyled at a re- 
mote period, so that there will have been ample time for 
some of the species to have been since rendered dice- 
cious. Asa Gray informs me that Coprosma is dicecious, 
and that it is closely allied through Nertera to Mitch- 
ella, which as we know is a heterostyled dimorphic 
species. In the male flowers of Coprosma the stamens 
are exserted, and in the female flowers the stigmas ; 
so that, judging from the affinities of the above three 
genera, it seems probable that an ancient short-styled 
form bearing long stamens with large anthers and 
large pollen-grains (as in the case of several Rubia- 
ceous genera) has been converted into the male Co- 
prosma; and that an ancient long-styled form with short 
stamens, small anthers and small pollen-grains has 
been converted into the female form. But according 
to Mr. Meehan,* Mitchella itself is dicecious in some 
districts; for he says that one form has small sessile 
anthers without a trace of pollen, the pistil being 
perfect ; while in another form the stamens are perfect 
and the pistil rudimentary. He adds that plants 
may be observed in the autumn bearing an abundant 
crop of berries, and others without a single one. 
Should these statements be confirmed, Mitchella will 
be proved to be heterostyled in one district and 
dicecious in another. 

Asperula is likewise a Rubiaceous genus, and from 
the published description of the two forms of A. sco- 
paria, an inhabitant of Tasmania, I did not doubt that 
it was heterostyled; but on examining some flowers 
sent me by Dr. Hooker they proved to be dicecious. 
The male flowers have large anthers and a very small 


+ Proce. Acad. of Sciences of Philadelphia, July 28, 1868, p. 183, 


286 DICECIOUS AND Cuap. VII. 


ovarium, surmounted by a mere vestige of a stigma 
without any style; whilst the female flowers possess 
a large ovarium, the anthers being rudimentary and 
apparently quite destitute of pollen. Considering 
how many Rubiaceous genera are heterostyled, it is a 
reasonable suspicion that this Asperula is descended 
from a heterostyled progenitor; but we should be 
cautious on this head, for there is no improbability in 
a homostyled Rubiaceous plant becoming dicecious. 
Moreover, in an allied plant, Galiwm ecruciatum, the 
female organs have been suppressed in most of the 
lower flowers, whilst the upper ones remain hermaph- 
rodite; and here we have a modification of the sexual 
organs without any connection with heterostylism. 

Mr. Thwaites informs me that in Ceylon various 
Rubiaceous plants are heterostyled ; but in the case 
of Discospermum one of the two forms is always 
barren, the ovary containing about two aborted ovules 
in each loculus; whilst in the other form each loculus 
contains several perfect ovules; so that the species 
appears to be strictly dicecious. 

Most of the species of the South American genus 
/Higiphila, a member of the Verbenacex, apparently 
are heterostyled; and both Fritz Miller and myself 
thought that this was the case with 4. obdurata, so 
closely did its flowers resemble those of the heterostyled 
species. But on examining the flowers, the anthers of 
the long-styled form were found to be entirely desti- 
tute of pollen and less than half the size of those in 
the other form, the pistil being perfectly developed. 
On the other hand, in the short-styled form the stig- 
mas are reduced to half their proper length, having 
also an abnormal appearance ; whilst the stamens are 
perfect. This plant therefore is dicecious; and we 
may, I think, conclude that a short-styled progenitor, 


Cnar. VIL. POLYGAMOUS PLANTS. 287 


bearing long stamens exserted beyond the corolla, 
has been converted into the male; and a long-styled 
progenitor with fully developed stigmas into the fe- 
male. 

From the number of bad pollen-grains in the small 
anthers of the short stamens of the long-styled form 
of Pulmonaria angustifolia, we may suspect that this 
form is tending to become female; but it does not 
appear that the other or short-styled form is becoming 
more masculine. Certain appearances countenance 
the belief that the reproductive system of Phlow subu- 
lata is likewise undergoing a change of some kind. 

I have now given the few cases known to me in 
which heterostyled plants appear with some consider- 
able degree of probability to have been rendered 
dicecious. Nor ought we to expect to find many such 
cases, for the number of heterostyled species is by no 
means large, at least in Europe, where they could 
hardly have escaped notice. Therefore the number of 
dicecious species which owe their origin to the trans- 
formation of heterostyled plants is probably not so 
large as might have been anticipated from the facilities 
which they offer for such conversion. 

In searching for cases like the foregoing ones, I have 
been led to examine some dicecious or sub-dicecious 
plants, which are worth describing, chiefly as they 
show by what fine gradations hermaphrodites may 
pass into polygamous or dicecious species. 


Polygamous, Dicecious and Sub-dicecious Plants. 


Euonymus Europeus (Celastrinee ).—The spindle-tree 
is described in all the botanical works which I have 
consulted as an hermaphrodite. Asa Gray speaks of 
the flowers of the American species as perfect, whilst 


288 DIGCIOUS AND Cuar. VIL 


those in the allied genus Celastrus are said to be 
“polygamo-diccious.” If a number of bushes of our 
spindle-tree be examined, about half will be found to 
have stamens equal in length to the pistil, with well- 
developed anthers; the pistil being likewise to all 
appearance well developed. The other half have a 
perfect pistil, with the stamens short, bearing rudi- 
mentary anthers destitute of pollen; so that these 
bushes are females. All the flowers on the same plant 
present the same structure. The female corolla is 
smaller than that on the polleniferous bushes. The 
two forms are shown in the accompanying drawings. 


Hermaphrodite or male. Female. 


EvoNyMvus EvUROPZUS. 


1 did not at first doubt that this species existed 
under an hermaphrodite and female form ; but we shall 
presently see that some of the bushes which appear 
to be hermaphrodites never produce fruit, and, these 
are in fact males. The species, therefore, is poly- 
gamous in the sense in which I use the term, and tri- 
oicous. The flowers are frequented by many Diptera 
and some small Hymenoptera for the sake of the 
nectar secreted by the disc, but I did not see a single 
bee at work; nevertheless the other insects sufficed to 


Cuar. VIL. POLYGAMOUS PLANTS. 289 


fertilise effectually female bushes growing at a dis- 
tance of even 30 yards from any polleniferous bush. 
The small anthers borne by the short stamens of 
the female flowers are well formed and dehisce pro- 
perly, but I could never find in them a single grain 
of pollen. It is somewhat difficult to compare the 
length of the pistils in the two forms, as they vary 
somewhat in this respect and gontinue to grow after 
the anthers are mature. The pistils, therefore, in old 
flowers on a polleniferous plant are often of consider- 
ably greater length than in young flowers on a female 
plant. On this account the pistils from five flowers 
from so mary hermaphrodite or male bushes were 
compared with those from five female bushes, before 
the anthers had dehisced and whilst the rudimentary 
ones were of a pink colour and not at all shrivelled. . 
These two sets of pistils did not differ in length, or if 
there was any difference those of the polleniferous 
flowers were rather the longest. In one hermaphrodite 
plant, which produced during three years very few 
and poor fruit, the pistil much exceeded in length 
the stamens bearing perfect and as yet closed an- 
thers; and I never saw such a case on any female 
plant. It is a surprising fact that the pistil in the 
male and in the semi-sterile hermaphrodite flowers 
has not been reduced in length, seeing that it per- 
forms very poorly or not at all its proper function. 
The stigmas in the two forms are exactly alike ; and 
in some of the polleniferous plants which never pro- 
duced any fruit I found that the surface of the stigma 
was viscid, so that pollen-grains adhered to it and had 
exserted their tubes. The ovules are of equal size 
in the two forms. Therefore the most acute botanist, 
judging only by structure, would never have suspected 


290 DIGCIOUS AND Cuar. VIL. 


that some of the bushes were in function exclusively 
males, 

Thirteen bushes growing near one another in a 
hedge consisted of eight females quite destitute of 
pollen and of five hermaphrodites with well-developed 
anthers. In the autumn the eight females were well 
covered with fruit, excepting one, which bore only a 
moderate number. Of the five hermaphrodites, one 
bore a dozen or two fruits, and the remaining four 
bushes several dozen ; but their number was as nothing 
compared with those on the female bushes, for a single 
branch, between two and three feet in length, from 
one of the latter, yielded more than any one of the 
hermaphrodite bushes. The difference in the amount 
of fruit produced by the two sets of bushes is all the 
more striking, as from the sketches above given it is 
obvious that the stigmas of the polleniferous flowers 
can hardly fail to receive their own pollen ; whilst the 
fertilisation of the female flowers depends on pollen 
being brought to them by flies and the smaller 
Hymenoptera, which are far from being such efficient 
carriers as bees. 

I now determined to observe more carefully during 
successive seasons some bushes growing in another 
place about a mile distant. As the female bushes 
were so highly productive, I marked only two of them 
with the letters A and B, and five polleniferous bushes 
with the letters C to G. I may premise that the 
year 1865 was highly favourable for the fruiting of all 
the bushes, especially for the polleniferous ones, some 
of which were quite barren except under such fayvour- 
able conditions. The season of 1864 was unfavourable. 
In 18638 the female A produced “ some fruit ;” in 1864 
only 9; and in 1865, 97 fruit. The female B in 1863 
was “ covered with fruit ;” in 1864 it bore 28; and in 


Cuapr. VIL. POLYGAMOUS PLANTS. 291 


1865 “innumerable very fine fruits.” I may add, 
that three other female trees growing close by were 
observed, but only during 1863, and they then bore 
abundantly. With respect to the polleniferous bushes, 
the one marked C did not bear a single fruit during 
the years 1863 and 1864, but during 1865 it produced 
no less than 92 fruit, which, however, were very poor. 
I selected one of the finest branches with 15 fruit, and 
these contained 20 seeds, or on an average 1°33 per 
fruit. I then took by hazard 15 fruit from an adjoin- 
ing female bush, and these contained 43 seeds; that 
is, more than twice as many, or on an average 2°86 
per fruit. Many of the fruits from the female bushes 
included four seeds, and only one had a single seed ; 
whereas not one fruit from the polleniferous bushes 
contained four seeds. Moreover when the two lots of 
seeds were compared, it was manifest that those from 
the female bushes were the larger. The second 
polleniferous bush, D, bore in 1863 about two dozen 
fruit,—in 1864 only 3 very poor fruit, each containing 
a single seed,—and in 1865, 20 equally poor fruit. 
Lastly, the three polleniferous bushes, EH, F, and G, 
did not produce a single fruit during the three years 
1863, 1864, and 1865. 

We thus see that the female bushes differ somewhat 
in their degree of fertility, and the polleniferous ones 
in the most marked manner. We have a _ perfect 
gradation from the female bush, B, which in 1865 was 
covered with “innumerable fruits,’ —through the 
female A, which produced during the same year 97,— 
through the polleniferous bush C, which produced 
this year 92 fruits, these, however, containing a very 
low average number of seeds of small size,—through 
the bush D, which produced only 20 poor fruit,—to 
the three bushes, E, F, and G, which did not this 


292 DIGCIOUS AND Cuap. VIL. 


year, or during the two previous years, produce a 
single fruit. If these latter bushes and the more 
fertile female ones were to supplant the others, the 
spindle-tree would be as strictly dicecious in function 
as any plant in the world. This case appears to me 
very interesting, as showing how gradually an herma- 
phrodite plant may be converted into a dicecious one.* 

Seeing how general it is for organs which are 
almost or quite functionless to be reduced in size, it is 
remarkable that the pistils of the polleniferous plants 
‘should equal or even exceed in length those of the 
highly fertile female plants. This fact formerly led 
me to suppose that the spindle-tree had once been 
heterostyled ; the hermaphrodite and male plants hay- 
ing been originally long-styled, with the pistils since 
reduced in length, but with the stamens retaining 
their former dimensions; whilst the female plant had 
been originally short-styled, with the pistil in its pre- 
sent state, but with the stamens since greatly reduced 
and rendered rudimentary. A conversion of this kind 
is at least possible, although it is the reverse of 
that which appears actually to have occurred with 
some Rubiaceous genera and Aigiphila; for with these 
plants the short-styled form has become the male, and 
the long-styled the female. It is, however, a more 
simple view that sufficient time has not elapsed for the 


* According to Fritz Muller 
(Bot. Zeitung,’ 1870, p. 151), a 
Chamissoa (Amaranthaceze) in 
Southern Brazil is in nearly the 
same state as our Euonymus. The 
ovules are equally developed in the 
two forms. In the female the pistil 
is perfect, whilst the anthers are 
entirely destitute of pollen. In 
the polleniferous form, the pistil 
is short and the stigmas never 


separate from one another, so 
that, although their surfaces are 
covered with fairly well-developed 
papille, they cannot be fertilised. 
These latter plants do not com- 
monly yield any fruit, and are 
therefore in function males. Never- 
theless, on one occasion Fritz 
Miiller found flowers of this kind in 
which the stigmas had separated, 
and they produced some fruit. 


Cuar. VIL. POLYGAMOUS PLANTS. 293 


reduction of the pistil in the male and hermaphrodite 
flowers of our Euonymus ; though this view does not 
account for the pistils in the polleniferous flowers 
being sometimes longer than those in the female 
flowers. 

Fragaria vesca, Virginiana, Chiloensis, de. (Rosacez). 
—A tendency to the separation of the sexes in the 
cultivated strawberry seems to be much more strongly 
marked in the United States than in Europe; and 
this appears to be the result of the direct action of 
climate on the reproductive organs. In the best ac- 
count which I have seen,* it is stated that many of the 
varieties in the United States consist of three forms, 
namely, females, which produce a heavy crop of fruit,— 
of hermaphrodites, which “seldom produce other than 
a very scanty crop of inferior and imperfect berries,” 
—and of males, which produce none. The most skilful 
cultivators plant “seven rows of female plants, then 
one row of hermaphrodites, and so -on throughout the 
field.” The males bear large, the hermaphrodites 
mid-sized, and the females small flowers. The latter 
plants produce few runners, whilst the two other forms 
produce many; consequently, as has been observed 
both in England and in the United States, the polleni- 
ferous forms increase rapidly and tend to supplant 
the females. We may therefore infer that much more 
vital force is expended in the production of ovules 
and fruit than in the production of pollen. Another 
species, the Hautbois strawberry (Lf. elatior), is more 
strictly dicecious; but Lindley made by selection an 
hermaphrodite stock. 

Rhamnus catharticus (Rhamnez).—This plant is well 


* Mr. Leonard Wray in‘Gard. information on this subject, see 
Chron.’ 1861, p. 716. ‘Variation under Domestication,’ 
¢ For references and further chap. x. 2nd edit. vol. i. p. 375. 


294 DIGCIOUS AND Cuap. VII. 


known to be diccious. My son William found the 
two sexes growing in about equal numbers in the Isle 
of Wight, and sent me specimens, together with obser- 
vations on them. Lach sex consists of two sub-forms. 
The two forms of the male differ in their pistils: 
in some plants it is quite small, without any distinct 
stigma; in others the pistil is much more developed, 
with the papill# on the stigmatic surfaces moderately 
large. The ovules in both kinds of males are in an 
aborted condition. On my mentioning this case to Pro- 
fessor Caspary, he examined several male plants in 
the botanic gardens at Kénigsberg, where there were 
no females, and sent me the accompanying drawings. 


Fig. 13. 


Long-styled male. Short-styled male. 
RHAMNUS CATHARTICUS. (From Caspary.) 


In the English plants the petals are not so greatly 
reduced as represented in this drawing. My son ob- 
served that those males which had their pistils mode- 
rately well developed bore slighly larger flowers, and, 
what is very remarkable, their pollen-grains exceeded 
by a little in diameter those of the males with greatly 
reduced pistils. This fact is opposed to the belief that 
the present species was once heterostyled; for in this 
case it might have been expected that the shorter- 
styled plants would haye had larger pollen-grains. 

In the female plants the stamens are in an ex- 
tremely rudimentary condition, much more so than 


Car. VIL. POLYGAMOUS PLANTS. 295 


the pistiis in the males. The pistil varies consi- 
derably in length in the female plants, so that they 
may be divided into two sub-forms according to the 


Fig. 14. 


q ad 


Long-styled Short-styled 
female, female. 


RHAMNUS CATHARTICUS. 


length of this organ. Both the petals and sepals are 
decidedly smaller in the females than in the males ; 
and the sepals do not turn downwards, as do those of 
the male flowers when mature. All the flowers on the 
same male or same female bush, though subject to 
some variability, belong to the same sub-form; and 
as my son never experienced any difficulty in decid- 
ing under which class a plant ought to be included, 
he believes that the two sub-forms of the same sex 
do not graduate into one another. I can form no 
satisfactory theory how the four forms of this plant 
originated. 

Rhamnus lanceolatus exists in the United States, 
as I am informed by Professor Asa Gray, under two 
hermaphrodite forms. In the one, which may be called 
the short-styled, the flowers are sub-solitary, and in- 
clude a pistil about two-thirds or only half as long as 
that in the other form; it has also shorter stigmas. The 
stamens are of equal length in the two forms; but the 
anthers of the short-styled contain rather less pollen, 
as far as I could judge from a few dried flowers. My 


296 DIGCIOUS AND Cuar. VIL. 


son compared the pollen-grains from the two forms, 
and those from the long-styled flowers were to those 
from the short-styled, on an average from ten measure- 
ments, as 10 to 9 in diameter; so that the two her- 
maphrodite forms of this ppesice resemble in this 
respect the two male forms of Lt. catharticus. The 
long-styled form is not so common as the short-styled. 
The latter is said by Asa Gray to be the more fruitful 
of the two, as might have been expected from its 
appearing to produce less pollen, and from the grains 
being of smaller size; it is therefore the more highly 
feminine of the two. The long-styled form produces 
a greater number of flowers, which are clustered to- 
gether instead of being sub-solitary; they yield some 
fruit, but as just stated are less fruitful than the other 
form, so that this form appears to be the more mas- 
culine of the two. On the supposition that we have 
here an hermaphrodite plant becoming dicecious, there 
are two points deserving notice; firstly, the greater 
length of the pistil in the incipient male form; and 
we have met with a nearly similar case in the male 
and hermaphrodite forms of Huonymus compared with 
the females. Secondly, the larger size of the pollen- 
grains in the more masculine flowers, which perhaps may 
be attributed to their having retained their normal size ; 
whilst those in the incipient female flowers have been 
reduced. The long-styled form of R.lanceolatus seems 
to correspond with the males of R. catharticus which 
have a longer pistil and larger pollen-grains. Light 
will perhaps be thrown on the nature of the forms 
in this genus, as soon as the power of both kinds of 
pollen on both stigmas is ascertained. Several other 
species of Rhamnus are said to be dicecious* or sub- 


* Lecoq, ‘Géogr. Bot.’ tom. v. 1856, pp. 420-26. 


Cuapr. VIL. POLYGAMOUS PLANTS. 297 


dicecious. On the other hand, R. frangula is an ordi- 
nary hermaphrodite, for my son found a large number 
of bushes all bearing an equal profusion of fruit. 

Epigea repens (Ericaceze).—This plant appears to 
be in nearly the same state as Rhamnus catharticus. 
It is described by Asa Gray* as existing under four 
forms. (1) With long style, perfect stigma, and short 
abortive stamens. (2) Shorter style, but with stigma 
equally perfect, short abortive stamens. These two 
female forms amounted to 20 per cent. of the speci- 
mens received from one locality in Maine; but all 
the fruiting specimens belonged to the first form. 
(3) Style long, as in No. 1, but with stigma imperfect, 
stamens perfect. (4) Style shorter than in the last, 
stigma imperfect, stamens perfect. These two latter 
forms are evidently males. Therefore, as Asa Gray 
remarks, “the flowers may be classified into two kinds, 
each with two modifications; the two main kinds 
characterised by the nature and perfection of the 
stigma, along with more or less abortion of the 
stamens; their modifications, by the length of the 
style.” Mr. Meehan has described the extreme 
variability of the corolla and calyx in this plant, and 
shows that it is dicecious. It is much to be wished 
that the pollen-grains in the two male forms should 
be compared, and their fertilising power tried on the 
two female forms. 

Tlea aquifolium (Aquifoliaceze).—In the several 
works which I have consulted, one author alonef says 
that the holly is dicecious. During several years I 


*¢ American JournalofScience, delphia,’ May 1868, p. 153. 
July 1876. Also ‘The American t Vaucher, ‘Hist. Phys. des 
Naturalist, 1876, p. 490. Plantes d’Europe,’ 1841, tom. ii, 
+ “Variationsin Epigaa repens,’ _p. 11. 
Proc. Acad. Nat. Soc. of Phila- 


298 GYNO-DI@CIOUS PLANTS. Cuap. VIL. 


have examined many plants, but have never found 
one that was really hermaphrodite. I mention this 
genus because the stamens in the female flowers, al- 
though quite destitute of pollen, are but slightly and 
sometimes not at all shorter than the perfect stamens 
in the male flowers. In the latter the ovary is small 
and the pistil is almost aborted. The filaments of the 
perfect stamens adhere for a greater length to the 
petals than in the female flowers. The corolla of 
the latter is rather smaller than that of the male. 
The male trees produce a greater number of flowers 
than the females. Asa Gray informs me that I. opaca, 
which represents in the United States our common 
holly, appears (judging from dried flowers) to be in a 
sunilar state ; and so it is, according to Vaucher, with 
several other but not with all the species of the genus. 


Gyno-dicecious Plants. 


The plants hitherto described either show a tendency 
to become dicecious, or apparently have become so 
within a recent period. But the species now to be 
considered consist of hermaphrodites and females 
without males, and rarely show any tendency to 
be dicecious, as far as can be judged from their 
present condition and from the absence of species 
having separated sexes within the same groups. 
Species belonging to the present class, which I have 
called gyno-dicecious, are found in various widely 
distinct families; but are much more common in the 
Labiate (as has long been noticed by botanists) than 
in any other group. Such cases have been noticed 
by myself in Thymus serpyllum and vulgaris, Satwreia 
hortensis, Origanum vulgare, and Mentha hirsuta ; and 
by others in. Nepeta glechoma, Mentha vulgaris and 


Cuap. VII. GYNO-DIGCIOUS PLANTS. 299 


aquatica, and Prunella vulgaris. In these two latter 
species the female form, according to H. Miller, is 
infrequent. ‘To these must be added Dracocephalum 
Moldavicum, Melissa officinalis and clinipodiwm, and 
Hyssopus officinalis.* In the two last-named plants the 
female form likewise appears to be rare, for I raised 
many seedlings of both, and all were hermaphrodites. 
It has already been remarked in the Introduction that 
andro-dicecious species, as they may be called, or those 
which consist of hermaphrodites and males, are ex- 
tremely rare, or hardly exist. 

Thymus serpyllum.—The hermaphrodite plants pre- 
sent nothing particular in the state of their reproduc- 
tive organs; and so it is in all the following cases. The 
females of the present species produce rather fewer 
flowers and have somewhat smaller corollas than the 
hermaphrodites ; so that near Torquay, where this 
plant abounds, I could, after a little practice, distin- 
guish the two forms whilst walking quickly past them. 
According to Vaucher, the smaller size of the corolla 
is common to the females of most or all of the above- 
mentioned Labiate. The pistil of the female, though 
somewhat variable in length, is generally shorter, 
with the margins of the stigma broader and formed 
of more lax tissue, than that of the hermaphrodite. 
The stamens in the female vary excessively in length ; 
they are generally enclosed within the tube of the 


* H. Miiller, ‘Die Befruchtung 
der Blumen,’ 1873; and ‘ Nature,’ 
1873, p. 161. Vaucher, ‘ Plantes 
d’Europe, tom. iii. p. 611. For 
Dracoceplialum, Schimper, as 
quoted by Braun, ‘Annals and 
Mag. of Nat. Hist.’ 2nd series, vol. 
xviii. 1856, p. 380, Lecoq, ‘ Géo- 
graphie Bot. de l Europe,’ tom. viii. 
pp. 33, 38, 44, &e. Both Vaucher 


and Leeoq were mistaken in think- 
ing that several of the plants 
named in the text are dioecious. 
They appear to have assumed that 
the hermaphrodite form was a 
male; perhaps they were de- 
ceived by the pistil not becoming 
fully developed and of proper 
length until some time after the 
anthers have dehisced. 


300 GYNO-DICGCIOUS. PLANTS. Cuar. Vil. 


corolla, and their anthers do not contain any sound 
pollen; but after long search I found a single plant 
with the stamens moderately exserted, and their 
anthers contained a very few full-sized grains, together 
with a multitude of minute empty ones. In some 
females the stamens are extremely short, and their 
minute anthers, though divided into the two normal 
cells or loculi, contained not a trace of pollen: in 
others again the anthers did not exceed in diameter 
the filaments which supported them, and were not 
divided into two loculi. Judging from what I have 
myself seen and from the descriptions of others, all 
the plants in Britain, Germany, and near Mentone, 
are in the state just described; and I have never 
found a single flower with an aborted pistil. It is, 
therefore, remarkable that, according to Delpino,* this 
plant near Florence is generally trimorphic, consisting 
of males. with aborted pistils, females with aborted 
stamens, and hermaphrodites. 

I found it very difficult to judge of the proportional 
number of the two forms at Torquay. They often 
grow mingled together, but with large patches con- 
sisting of one form alone. At first I thought that the 
two were nearly equal in number; but on examining 
every plant which grew close to the edge of a little 
overhanging dry cliff, about 200 yards in length, 1 
found only 12 females; all the rest, some hundreds 
in number, being hermaphrodites. Again, on an 
extensive gently sloping bank, which was so thickly 
covered with this plant that, viewed from the distance 
of half a mile it appeared of a pink colour, I could 
not discover a single female. Therefore the her- 


* ¢Sull’ Opera,la Distribuzione H. Miiller, ‘Die Befruchtung,’ 
dei Sessi nelle Piante, &c.’ 1867, &e.,’ p. 27. 
p. 7. With respect to Germany, 


Cap. VII. GYNO-DIGCIOUS PLANTS. 301 


maphrodites must greatly exceed. in number the 
females, at least in the localities examined by me. 
A very dry station apparently favours the presence 
of the female form. With some of the other above- 
named Labiate the nature of the soil or climate 
likewise seems to determine the presence of one or 
both forms; thus with Nepeta glechoma, Mr. Hart found 
in 1873 that all the plants which he examined near 
Kilkenny in Ireland were females; whilst all near 
Bath were hermaphrodites, and near Hertford both 
forms were present, but with a preponderance of her- 
maphrodites.* It would, however, be a mistake to 
suppose that the nature of the conditions determines 
the form independently of inheritance; for I sowed 
in the same small bed seeds of T. serpyllum, gathered 
at Torquay from the female alone, and these produced 
an abundance of both forms. There is every reason 
to believe, from large patches consisting of the same 
form, that the same individual plant, however much 
it may spread, always retains the same form. In two 
distant gardens I found masses of the lemon-thyme 
(T. citriodorus, a var. of T. serpyllum), which I was 
informed had grown there during many years, and 
every flower was female. 

With respect to the fertility of the two forms, I 
marked at Torquay a large hermaphrodite and a large 
female plant of nearly equal sizes, and when the seeds 
were ripe I gathered all the heads. The two heaps 
were of very nearly equal bulk; but the heads from 
the female plant numbered 160, and their seeds 
weighed 8°7 grains; whilst those from the her- 
maphrodite plant numbered 200, and their seeds 
weighed only 4:9 grains; so that the seeds from the 


* ‘Nature, June 1873, p. 162. 


302 GYNO-DIGCIOUS PLANTS. Cuap. VII. 


female plant were to those from the hermaphrodite 
as 100 to 56 in weight. If the relative weight of 
the seeds from an equal number of flower-heads from 
the two forms be compared, the ratio is as 100 for the 
female to 45 for the hermaphrodite form. 

Thymus vulgaris—The common garden thyme re- 
sembles in almost every respect T. serpyllum. The 
same slight differences between the stigmas of the 
two forms could be perceived. In the females the 
stamens are not generally quite so much reduced as 
in the same form of T. serpyllum. In some specimens 
sent me from Mentone by Mr. Moggridge, together 
with the accompanying sketches, the anthers of the 


Fig. 15. 


Hermaphrodite. Females. 


THYMUS VULGARIS (magnified), 


female, though small, were well formed, but they con- 
tained very little pollen, and not a single sound grain 
could be detected. Highteen seedlings were raised 
from purchased seed, sown in the same small’ bed ; 
and these consisted of seven hermaphrodites and 
eleven females. They were left freely exposed to 
the visits of bees, and no doubt every female flower 
was fertilised; for on placing under the micro- 
scope a large number of stigmas from female plants, 


Cuar. VII GYNO-DIGCIOUS PLANTS. 303 


not one could be found to which pollen-grains of 
thyme did not adhere. The seeds were carefully 
collected from the eleven female plants, and they 
weighed 98:7 grains; and those from the seven her- 
maphrodites 36°5 grains. This gives for an equal 
number of plants the ratio of 100 to 58; and we 
here see, as in the last case, how much more fertile 
the females are than the hermaphrodites. These two 
- lots of seeds were sown separately in two adjoining 
beds, and the seedlings from both the hermaphro- 
dite and female parent-plants consisted of both forms. 
Satureia hortensis.—Eleven seedlings were raised in 
separate pots in a hotbed and afterwards kept in the 
green-house. They consisted of ten females and of 
a single hermaphrodite. Whether or not the condi- 
tions to which they had been subjected caused the great 
excess of females I do not know. In the females the 
pistil is rather longer than that of the hermaphrodite, 
and the stamens are mere rudiments, with minute 
colourless anthers destitute of pollen. The windows 
of the green-house were left open, and the ficwers 
were incessantly visited by humble and hive bees. 
Although the ten females did not produce a single 
grain of pollen, yet they were all thoroughly well 
fertilised by the one hermaphrodite plant, and this 
is an interesting fact. It should be added that no 
other plant of this species grew in my garden. The 
seeds were collected from the finest female plant, 
and they weighed 78 grains; whilst those from the 
hermaphrodite, which was a rather Jarger plant than 
the female, weighed only 33-2 grains; that is, in the 
ratio of 100 to 45. The female form, therefore, is very 
much more fertile than the hermaphrodite, as in the two 
last cases ; but the hermaphrodite was necessarily self- 
fertilised, and this probably diminished its fertility. 
14 


304 GYNO-DICECIOUS PLANTS. Cuap. VIL. 


We may now consider the probable means by which 
so many of the Labiatze have been separated into two 
forms, and the advantages thus gained. H. Miller* 
supposes that originally some individuals varied so as 
to produce more conspicuous flowers; and that imsects 
habitually visited these first, and then dusted with - 
their pollen visited and fertilised the less conspicuous 
flowers. The production of pollen by the latter plants 
would thus be rendered superfluous, and it would be 
advantageous to the species that their stamens should 
abort, so as to save useless expenditure. They would 
thus be converted into females. But another view may 
be suggested: as the production of a large supply of 
seeds evidently is of high importance to many plants, 
and. as we have seen in the three foregoing cases 
that the females produce many more seeds than the 
hermaphrodites, increased fertility seems to me the 
more probable cause of the formation and separation of 
the two forms. From the data above given it follows 
that ten plants of Thymus serpyllum, if half consisted 
of hermaphrodites and half of females, would yield 
seeds compared with ten hermaphrodite plants in the 
ratio of 100 to 72. Under similar circumstances the 
ratio with Satureta hortensis (subject to the doubt from 
the self-fertilisation of the hermaphrodite) would be as 
100 to 60. Whether the two forms originated in cer- 
tain individuals varying and producing more seed than 
usual, and consequently producing less pollen; or in 
the stamens of certain individuals tending from some 
unknown cause to abort, and consequently producing 
more seed, it is impossible to decide; but in either 
case, if the tencency to the increased production of 
seed were steadily favoured, the result would be the 


« ‘Die Befruchtung der Blumen,’ pp. 319, 326. 


Cuapr. VII. GYNO-DIGCIOUS PLANTS. 305 


complete abortion of the male organs. I shall pre- 
sently discuss the cause of the smaller size of the 
female corolla. 


Scabiosa arvensis (Dipsacex).—It has been shown by H. Miiller 
that this species exists in Germany under an hermaphrodite and 
female form.* In my neighbourhood (Kent) the female plants 
do not nearly equal in number the hermaphrodites. The stamens 
of the females vary much in their degree of abortion; in some 
plants they are quite short and produce no pollen; in others 
they reach to the mouth of the corolla, but their anthers are not 
half the proper size, never dehisce, and contain but few pollen- 
grains, these being colourless and of small diameter. The her- 
maphrodite flowers are strongly proterandous, and H. Miiller 
shows that, whilst all the stigmas on the same flower-head are 
mature at nearly the same time, the stamens dehisce one after 
the other; so that there is a great excess of pollen, which serves 
to fertilise the female plants. As the production of pollen by 
one set of plants is thus rendered superfluous, their male organs 
have become more or less completely aborted. Should it be 
hereafter proved that the female plants yield, as is probable, 
more seeds than the hermaphrodites, I should be inclined to 
extend the same view to this plant as to the Labiate. I have 
also observed the existence of two forms in our endemic S. 
succisa, and in the éxotic S. atro-purpurea. In the latter plant, 
differently to what occurs in S. arvensis, the female flowers, 
especially the larger circumferential ones, are smaller than those 
of the hermaphrodite form. According to Lecoq, the female 
flower-heads of S. succisa are likewise smaller than those of 
what he calls the male plants, but which are probably her- 
maphrodites. 

Echium vulgare (Boraginez).—The ordinary hermaphrodite 
form appears to be proterandrous, and nothing more need be said 
about it. The female differs in having a much smaller corolla | 
and shorter pistil, but a well-developed stigma. The stamens 


* *Befruchtung der Blumen,’ and females co-exist; it is, how- 
&c., p. 368. The two forms occur ever, possible that he may have 
not only in Germany, but in been deceived by the flowers being 
England and France. Lecoq, so strongly proterandrous. From 
(‘Géographie Bot.’ 1857, tom. vi. what Lecoq says, S. succisa like- 
pp. 473, 477) says that male wise appears to occur under two 
plants as well as hermaphrodites forms in France. 


306 GYNO-DI@CIOUS PLANTS. Cuap. VII 


are short; the anthers do not contain any sound pollen-grains, 
but in their place yellow incoherent cells which do not swell 
in water. Some plants were in an intermediate condition; that 
is, had one or two or three stamens of proper length with per- 
fect anthers, the other stamens being rudimentary. In one such 
plant half of one anther contained green perfect pollen-grains, 
and the other half yellowish-green imperfect grains. Both forms 
produced seed, but I neglected to observe whether in equal 
numbers. As I thought that the state of the anthers might be 
due to some fungoid growth, I examined them both in the bud 
and mature state, but could find no trace of mycelium. In 1862 
many female plants were found; and in 1864, 32 plants were 
collected in two localities, exactly half of which were hermaphro- 
dites, fourteen were females, and two in an intermediate con- 
dition. In 1866, 15 plants were collected in another locality, 
and these consisted of four hermaphrodites and eleven females. 
I may add that this season was a wet one, which shows that the 
abortion of the stamens can hardly be due to the dryness of the 
sites where the plants grew, as I at one time thought pro- 
bable. Seeds from an hermaphrodite were sown in my garden, 
and of the 23 seedlings raised, one belonged to the intermediate 
form, all the others being hermaphrodites, though two or three 
of them had unusually short stamens. I have consulted several 
botanical works, but have found no record of this plant varying 
in the manner here described. 

Plantago lanceolata (Plantaginese).—Delpino states that this 
plant presents in Italy three forms, which graduate from an 
anemophilous into an entomophilous condition. According to 
H. Miiller,* there are only two forms in Germany, neither of 
which show any special adaptation for insect fertilisation, and 
both appear to be hermaphrodites. But I have found in twe 
localities in England female and hermaphrodite forms existing 
together; and the same fact has been noticed by others.t The 
females are less frequent than the hermaphrodites; their stamens 
are short, and their anthers, which are of a brighter green 
whilst young than those of the other form, dehisce properly, yet 
contain either no pollen, or a small amount of imperfect grains 
of variable size. All the flower-heads on a plant belong to 


* ‘Die Befruchtung,’ &., p.342, Mr. W. Marshall writes to me to 
+ Mr. C. W. Crocker in ‘The _ the same effect from Ely. 
Gardener’s Chronicle,’ 1864, p. 294. 


Cuar. VII. © SIZE OF THE COROLLA. 307 


the same form. It is well known that this species is strongly 
proterogynous, and I found that the protruding stigmas of both 
the hermaphrodite and female flowers were penetrated by pollen- 
tubes, whilst their own anthers were immature and had not 
* escaped out of the bud. Plantago media does not present two 
forms; but it appears from Asa Gray’s description,* that such 
is the case with four of the North American species. The co- 
rolla does not properly expand in the short-stamened form of 
these plants. 

Cnicus, Serratula, Eriophorum.—tiIn the Composite, Cnicus 
palustris and acaulis are said by Sir J. E. Smith to exist as her- 
maphrodites and females, the former being the more frequent. 
With Serratula tinctoria a regular gradation may be followed 
from the hermaphrodite to the female form; in one of the latter 
plants the stamens were so tall that the anthers embraced the 
style as in the hermaphrodites, but they contained only a few 
grains of pollen, and these in an aborted condition; in an- 
other female, on the other hand, the anthers were much more 
reduced in size than is usual. Lastly, Dr. Dickie has shown 
that with Eriophorum angustifolium (Cyperacee) hermaphro- 
dite and female forms exist in Scotland and the Arctic regions, 
both of which yield seed. + 


It is a curious fact that in all the foregoing poly- 
_ gamous, dicecious, and gyno-dicecious plants in which 
any difference has been observed in the size of the 
corolla in the two or three forms, it is rather larger in 
the females, which have their stamens more or less or 
quite rudimentary, than in the hermaphrodites or males. 
This holds good with Euonymus, Rhamnus eatharticus, 
Nex, Fragaria, all or at least most of the before-named 
Labiatee, Scabiosa atro-purpurea, and Echium vulgare. 
So it is, according to Von Mohl, with Cardamine 


* «Manual of the Botany of 1862, p. 53. 
the N. United States,’ 2nd edit. + Sir J. E. Smith, ‘ Trans. 
1856, p. 269. Seealso‘ American Linn. Soc.’ vol. xiii. p. 599, 
Journal of Science, Noy. 1862, Dr. Dickie, ‘ Journal Linn. Soc. 
p. 419, and ‘Proc. American Bot.’ vol. ix. 1865, p. 161. 
Academy of Science, Oct. 14, 


308 SIZE OF THE COROLLA. Cuapr. VIL. 


amara, Geranium sylvaticum, Myosotis, and Salvia. 
On the other hand, as Von Mohl remarks, when a 
plant produces hermaphrodite flowers and _ others 
which are males owing to the more or less complete 
abortion of the female organs, the corollas of the 
males are not at all increased in size, or only excep- 
tionally and in a slight degree, as in Acer.* It seems 
therefore probable that the decreased size of the female 
corollas in the foregoing cases is due to a tendency to 
abortion spreading from the stamens to the petals. We 
see how intimately these organs are related in double 
flowers, in which the stamens are readily conyerted 
into petals. Indeed some botanists believe that petals 
do not consist of leaves directly metamorphosed, but of 
metamorphosed stamens. That the lessened size of the 
corolla in the above case is in some manner an indirect 
result of the modification of the reproductive organs is 
supported by the fact that in Rhamnus catharticus not 
only the petals but the green and inconspicuous sepals 
of the female have been reduced in size; and in the 
strawberry the flowers are largest in the males, mid- 
sized in the hermaphrodites, and smallest in the fe- 
males. These latter cases,—the variability in the size 
of the corolla in some of the above species, for instance 
in the common thyme,—together with the fact that it 
never differs greatly in size in the two forms—make 
me doubt much whether natural selection has come 
into play ;—that is whether, in accordance with H. 
Miiller’s belief, the advantage derived from the pol-_ 
leniferous flowers being visited first by insects has 
been sufficient to lead to a gradual reduction of the 
corolla of the female. We should bear in mind that as 
the hermaphrodite is the normal form, its corolla has 


* + Bot. Zeitung,’ 1863, p. 326. 


Cuap. VII. 


SIZE OF THE COROLLA. 


309 


probably retained its original size.* An objection to 
the above view should not be passed over; namely, that 
the abortion of the stamens in the females ought to 
have added through the law of compensation to the 
size of the corolla; and this perhaps would have oc- 
curred, had not the expenditure saved by the abor- 
tion of the stamens been directed to the female repro- 
ductive organs, so as to give to this form increased 


fertility. 


* Tt does not appear to me 
that Kerner’s view (‘ Die Schutz- 
mittel des Pollens, 1873, p. 56) 
can be accepted in the present 
cases, namely that the larger 
corolla in the hermaphrodites and 


males serves to protect their pollen 
from rain. In the genus Thymus, 
for instance, the aborted anthers 
of the female are much better 
protected than the perfect ones of 
the hermaphrodite. 


310 CLEISTOGAMIC FLOWERS. Cuar. VIII, 


CHAPTER VIII. 
CLEISTOGAMIC FLOWERS. 


General character of cleistogamic flowers—List of the genera producing 
such flowers, and their distribution in the vegetable series—Viola, 
description of the cleistogamic flowers in the several species, their 
fertility compared with that of the perfect flowers—Oxalis 
acetosella—O. sensitiva, three forms of cleistogamic flowers—Van- 
dellia—Ononis—Impatiens—Drosera—Miscellaneous observations 
or. various other cleistogamic plants—Anemophilous species produc- 
ing cleistogamic flowers—Leersia, perfect flowers rarely developed 
--Summary and concluding remarks on the origin of cleistogamic 
flowers—The chief conclusions which may be drawn from the 
observations in this volume. 

Ir was known even before the time of Linneus that 

certain plants produced two kinds of flowers, ordi- 

nary open, and minute closed ones; and this fact 
formerly gave rise to warm controversies about the 
sexuality of plants. These closed flowers have been 
appropriately named cleistogamic by Dr. Kuhn.* 
They are remarkable from their small size and from 
never opening, so that they resemble buds; their petals 
are rudimentary or quite aborted; their stamens are 
often reduced in number, with the anthers of very 
small size, containing few pollen-grains, which have 
remarkably thin transparent coats, and generally emit 
their tubes whilst still enclosed within the anther- 
cells ; and, lastly, the pistil is much reduced in size, 
with the stigma in some cases hardly at all developed. 

These flowers do not secrete nectar or emit any odour ; 

from their small size, as well as from the corolla being 


rudimentary, they are singularly inconspicuous. Con- 


* ‘Bot. Zeitung, 1867, p. 65. 


Cuar. VIII. CLEISTOGAMIC FLOWERS. or 


sequently insects do not visit them; nor if they did, 
could they find an entrance. Such flowers are therefore 
invariably self-fertilised ; yet they produce an abund- 
ance of seed. In several cases the young capsules 
bury themselves beneath the ground, and the seeds 
are there matured. These flowers are developed before, 
or after, or simultaneously with the perfect ones. 
Their development seems to be largely governed by 
the conditions to which the plants are exposed, for 
during certain seasons or in certain localities only 
cleistogamic or only perfect flowers are produced. 

Dr. Kuhn, in the article above referred to, gives a 
list of 44 genera including species which bear flowers 
of this kind. To this list I have added some genera, 
and the authorities are appended in a foot-note. I 
have omitted three names, from reasons likewise given 
in the foot-note. But it is by no means easy to de- 
cide in all cases whether certain flowers ought to be 
ranked as cleistogamic. For instance, Mr. Bentham 
informs me that in the South of France some of the 
flowers on the vine do not fully open and yet set 
fruit; and I hear from two experienced gardeners that 
this is the case with the vine in our hot-houses; but 
as the flowers do not appear to be completely closed it 
would be imprudent to consider them as cleistogamic. 
The flowers of some aquatic and marsh plants, for 
instance of Lanunculus aquatilis, Alisma natans, 
Subularia, Hlecebrum, Menyanthes, and Euryale,* 
remain closely shut as long as they are sub- 
merged, and in this condition fertilise themselves. 


* Delpino,‘ Sull’ Opera, laDistri- vol. iii. 1825, p. 157. For the 
buzione dei Sessi nelle Piante,’ &c. | behaviour of Menyanthes in Russia 
1867, p. 30. Subularia, however, see Gillibert in ‘Act. Acad. St. Pe- 
sometimes has its flowers fully  tersb.,’ 1777, part ii. p. 45.—On 
expanded beneath the water,see  Euryale, ‘Gardeners Chronicle, 
Sir J. E. Smith, ‘English Flora,’ 1877, p. 280. 


312 CLEISTOGAMIC FLOWERS. Cuar. VIL. 


They behave in this manner, apparently as a protec- 
tion to their pollen, and produce open flowers when 
exposed to the air; so that these cases seem rather 
different from those of true cleistogamic flowers, and 
have not been included in the list. Again, the flowers 
of some plants which are produced yery early or very 
late in the season do not properly expand; and these 
might perhaps be considered as incipiently cleisto- 
gamic; but as they do not present any of the remark- 
able peculiarities proper to the class, and as I have 
not found any full record of such cases, they are not 
entered in the list. When, however, it is believed on 
fairly good evidence that the flowers on a plant in its 
native country do not open at any hour of the day or 
night, and yet set seeds capable of germination, these 
may fairly be considered as cleistogamic, notwith- 
standing that they present no peculiarities of struc- 
ture. I will now give as complete a list of the genera 
containing cleistogamic species as I have been able 
to collect. 


TABLE 38. 

List of Genera including Cleistogamic Species (chiefly after Kuhn).” 
DICOTYLEDONS. DICOTYLEDONS. 
Eritrichium (Boraginez). Dedalacanthus (Acanthacez). 

Cuscuta (Convolyulacez). Dipteracanthus ss 
Scrophularia (Scrophularinez). /Echmanthera oa 
Linaria “8 Ruellia 

Vandellia + Lamium (Labiate). 
Cryphiacanthus (Acanthacez). Salvia & 
Eranthemum + Oxybaphus (Nyctaginez). 


* T have omitted Trifolium and 
Arachis from the list, because Von 
Mohl says (‘ Bot. Zeitung,’ 1863, 
p. 312) that the flower-stems 
merely draw the flowers beneath 
the ground, and that these do not 
appear to be properly cleistogamic. 
Correa de Mello (‘Journal Linn. 
Soc. Bot.’ vol. xi. 1870, p. 254) 
observed plants of Arachis in 


Brazil, and could never find such 
flowers. Plantago hasbeen omitted 
because as far as I can discover it 
produces hermaphrodite and fe- 
male flower-heads, but not cleis- 
togamic flowers. Krascheninikowia 
(vel Stellaria) has been omitted 
because it seems very doubtful 
from Maximowiez’ description 
whether the lower flowers which 


Cuar. VILL. 


CLEISTOGAMIC FLOWERS. 


TABLE 38—continued. 


: DICOTYLEDONS. 
Nyctaginia (Nyctaginez). 
Stapelia (Asclepiade). 
Specularia (Campanulacez). 
Campanula 
Hottonia (Prifnulacez). 
Anandria (Composite). 
Heterocarpxa (Crucifere). 
Viola (Violacez). 
Helianthemum pag oh 
Lechea 
Pavonia (Malvacez).. 
Gaudichaudia (Malpighiacez). 


Aspicarpa ” 
Camarea -- 
Janusia 


Polygala (Poly galex). 
Impatiens (Balsaminez). 
Oxalis (Geraniacez). 
Ononis (Leguminosz). 
Parochetus ., 
Chapmannia _,, 
Stylosanthus _,, 


DICOTYLEDONS, 
Lespedeza (Leguminosz). 
Vicia nD 
Lathyrus - 
Martinsia vel 
Neurocarpum f ” 
Amphicarpea ,, 


Glycine =f 
Galactia ~ 
Voandzeia of 


Drosera (Droseracee). 


MONOCOTYLEDONS. 


Juncus (Juncez). 

Leersia (Graminez), 
Hordeum A 
Cryptostachys ,, 
Commelina (Commelinez). 
Monochoria (Pontederacez). 
Schomburgkia (Orchidez). 


Cattleya 5 
Epidendron =F 
Thelymitra = 


have no petajJs or very small ones, 
and barren stamens or none, are 
cleistogamic; the upper herma- 
phrodite flowers are said never to 
produce fruit, and therefore pro- 
bably act as males. Moreover in 
Stellaria graminea, as Babington 
remarks (‘ British Botany,’ 1851, 
p. 51) “shorter and longer petals 
accompany an imperfection of the 
stamens or germen.” 

Ihave added to the list the fol- 
lowing cases: Several Acanthacezx, 
for which see J. Scott in ‘ Journal 
of Bot” (London), new series, vol. 
i. 1872, p. 161. With respect to 
Salvia see Dr. Ascherson in ‘ Bot. 
Zeitung,’ 1871, p.555. For Oxy- 
baphus and Nyctaginia see Asa 
Gray in ‘American Naturalist,’ 
Noy. 1873, p. 692. From Dr, 
Torrey’s account of  Hottonia 

ta ( Bull. of Torrey Botan. 
Club,’ vol. ii. June 1871) it is 
manifest that this plant produces 
true cleistogamic flowers. For 


Payonia see Bouché in ‘ Sitzungs- 
berichte d. Gesellsch. Natur, 
Freunde,’ Oct. 20, 1874, p. 90. I 
have added Thelymitra,as from the 
account given by Mr. Fitzgerald in 
his magnificent work on ‘ Austra- 
lian Orchids’ it appears that the 
flowers of this plant in its native 
home never open, but they do not 
appear to bereducedinsize. Nor 
is this the case with the flowers of 
certain species of Epidendron, 
Cattleya, &e. (see second edition 
of my ‘ Fertilisation of Orchids,’ 
p- 147), which without expanding 
produce capsules. It is therefore 
doubtful whether these Orchideze 
ought to have been incladed in the 
list. From what Duval-Jouve says 
about Cryptostachys in ‘ Bull. 
Soc. Bot. de France, tom. x. 1863, 
p- 195, this plant appears to pro- 
duce cleistogamic flowers. The 
other additions to the list are 
noticed in my text. 


314 CLEISTOGAMIC FLOWERS. Cuar. VILL, 


The first point that strikes us in considering this list 
of 550 genera, is that they are very widely distributed 
in the vegetable series. They are more common in the 
family of the Leguminose than in any other, and next 
in order in that of the Acanthacez and Malpighiacez. 
A large number, but not all the species, of certain 
genera, as of Oxalis and Viola, bear cleistogamic as 
well as ordinary flowers. A second point which de- 
serves notice is that a considerable proportion of the 
genera produce more or less irregular flowers; this is 
the case with about 32 out of the 55 genera, but to this 
subject I shall recur. 

I formerly made many observations on cleistogamic 
flowers, but only a few of them are worth giving, since 
the appearance of an admirable paper by Hugo von 
Mohl,* whose examination was in some respects much 
more complete than mine. His paper includes also an 
interesting history of our knowledge on the subject. 

Viola canina.—The calyx of the cleistogamic flowers 
differs in no respect from that of the perfect ones. The 
petals are reduced to five minute scales; the lower one, 
which represents the lower lip, is considerably larger 
than the others, but with no trace of the spur-like 
nectary; its margins are smooth, whilst those of the 
other four scale-like petals are papillose. D. Miller of 
Upsala says that in the specimens which he observed 
the petals were completely aborted.{ The stamens are 
very small, and only the two lower ones are provided 
with anthers, which do not cohere together as in the 
perfect flowers. The anthers are minute, with the two 
cells or loculi remarkably distinct; they contain very 
little pollen in comparison with those of the perfect 


* «Bot. Zeitung,’ 1863, p.309- paper contains the first full and 
28. satisfactory account of any cleisto- 
+ Ibid. 1857, p. 730. This  gamic flower. 


Guar. VIII. VIOLA. 315 


flowers. The connective expands into a membranous 
hood-like shield which projects above the anther-cells. 
These two lower stamens have no vestige of the curious 
appendages which secrete nectar in the perfect flowers. 
The three other stamens are destitute of anthers and 
have broader filaments, with their terminal membran- 
ous expansions flatter or not so hood-like as those of 
the two antheriferous stamens. The pollen-grains have 
remarkably thin transparent coats; when exposed to 
the air they shrivel up quickly ; when placed in water 
they swell, and are then $530 of an inch in diameter, 
and therefore of smaller size than the ordinary pollen- 
grains similarly treated, which have a diameter of 
~~) of an inch. In the cleistogamic flowers, the 
pollen-grains, as far as I could see, never naturally fall 
out of the anther-cells, but emit their tubes through a 
pore at the upper end. I was able to trace the tubes 
from the grains some way down the stigma. The pistil 
is very short, with the style hooked, so that its ex- 
tremity, which is a little enlarged or funnel-shaped 
and represents the stigma, is directed downwards, 
being covered by the two membranous expansions of 
the antheriferous stamens. It is remarkable that there 
is an open passage from the enlarged funnel-shaped 
extremity to within the ovarium ; this was evident, as 
slight pressure caused a bubble of air, which had been 
drawn in by some accident, to travel freely from one 
end to the other: a similar passage was observed by 
Michalet in V. alba. The pistil therefore differs con- 
siderably from that of the perfect flower; for in the 
latter it is much longer, and straight with the excep- 
tion of the rectangularly bent stigma; nor is it per- 
forated by an open passage. 

The ordinary or perfect flowers have been said by 
some authors never to produce capsules; but this is an 


316 CLEISTOGAMIC FLOWERS. Cuap. VILL. 


error, though only a small proportion of them do so. 
This appears to depend in some cases on their anthers 
not containing even a trace of pollen, but more gene- 
rally on bees not visiting the flowers. I twice covered 
with a net a group of flowers, and marked with threads 
twelve of them which had not as yet expanded. ‘This 
precaution is necessary, for though as a general rule 
the perfect flowers appear considerably- before the 
cleistogamic ones, yet occasionally some of the latter 
are produced early in the season, and their capsules 
might readily be mistaken for those produced by the 
perfect flowers. Not one of the twelve marked perfect 
flowers yielded a capsule, whilst others under the net 
which had been artificially fertilised produced five 
capsules ; and these contained exactly the same aver- 
age number of seeds as some capsules from flowers 
outside the net which had been fertilised by bees. I 
have repeatedly seen Bombus hortorwm, lapidarius, and 
a third species, as well as hive-bees, sucking the 
flowers of this violet: I marked six which were thus 
visited, and four of them produced fine capsules; the 
two others were gnawed off by some animal. I 
watched Bombus hortorum for some time, and when- 
ever it came to a flower which did not stand in a con- 
venient position to be sucked, it bit a hole through the 
spur-like nectary. Such ill-placed flowers would not 
yield any seed or leave descendants ; and the plants 
bearing them would thus tend to be eliminated through 
natural selection. 

The seeds produced by the cleistogamic and perfect 
flowers do not differ in appearance or number. On 
two occasions I fertilised several perfect flowers with 
pollen from other individuals, and afterwards marked 
some cleistogamic flowers on the same plants; and the 
result was that 14 capsules produced by the perfect 


Cuar. VILL. VIOLA. SLT 


flowers contained on an average 9°85 seeds; and 17 
capsules from the cleistogamic ones contained 9°64 
seeds,—an amount of difference of no significance. It 
is remarkable how much more quickly the capsules 
from the cleistogamic flowers are developed than those 
from the perfect ones; for instance, several perfect 
flowers were cross-fertilised on April 14th, 1863, and a 
month afterwards (May 15th) eight young cleistogamic 
flowers were marked with threads; and when the two 
sets of capsules thus produced were compared on 
June 38rd, there was scarcely any difference between 
them in size. 

Viola odorata (white-flowered, single, cultivated va- 
riety).—The petals are represented by mere scales as 
in the last species; but differently from in the last, 
all five stamens are provided with diminutive anthers. 
Small bundles of pollen-tubes were traced from the 
five anthers into the somewhat distant stigma. The 
capsules produced by these flowers bury themselves in 
the soil, if it be loose enough, and there mature them- 
selyes.* Lecoq says that it is only these latter cap- 
sules which possess elastic valves; but I think this 
must be a misprint, as such valves would obviously be 
of no use to the buried capsules, but would serve to 
scatter the seeds of the sub-aerial ones, as in the other 
species of Viola. It is remarkable that this plant, ac- 
cording to Delpino,t does not produce cleistogamic 
flowers in one part of Liguria, whilst the perfect flowers 
are there abundantly fertile; on the other hand, 
cleistogamic flowers are produced by it near Turin. 
Another fact is worth giving as an instance of corre- 


* Vaucher says (‘Hist. Phys.des tom. v. 1856, p. 180. 


Plantes d’Europe,’ tom. iii. 1844, + ‘Sul’ Opera, la Distribuzione 
p. 309) that V. hirta and collina dei Sessi nelle Piante, &c., 1867, 
likewise bury their capsules.— _ p. 30. 


See also Lecoq, ‘Géograph. Bot.’ 


318 CLEISTOGAMIC FLOWERS. Cuar. Viil 


lated development: I found on a purple variety, 
after it had produced its perfect double flowers, and 
whilst the white single variety was bearing its cleisto- 
gamic flowers, many bud-like bodies which from their 
position on the plant were certainly of a cleistogamic 
nature. They consisted, as could be seen on bisecting 
them, of a dense mass of minute scales closely folded 
over one another, exactly like a cabbage-head in 
miniature. I could not detect any stamens, and in the 
place of the ovarium there was a little central column. 
‘The doubleness of the perfect flowers had thus spread 
to the cleistogamic ones, which therefore were ren- 
dered quite sterile. 

Viola hirta.—The five stamens of the cleistogamic 
flowers are provided, as in the last case, with small 
anthers, from all of which pollen-tubes proceed to the 
stigma. The petals are not quite so much reduced 
as in V. canina, and the short pistil instead of being 
hooked is merely bent into a rectangle. Of several 
perfect flowers which I saw visited by hive- and humble- 
bees, six were marked, but they produced only two 
capsules, some of the others having been accidentally 
injured. M. Monnier was therefore mistaken in this 
case as in that of V. odorata, in supposing that the 
perfect flowers always withered away and aborted. He 
states that the peduncles of the cleistogamic flowers 
curve downwards and bury the ovaries beneath the 
soil.* I may here add that Fritz Miller, as I hear 
from his brother, has found in the highlands of South- 
ern Brazil a white-flowered species of violet which 
bears subterranean cleistogamic flowers. 


* These statements are taken to the supposed sterility of the 
from Professor Oliver’s excellent perfect flowers in this genus see 
article in the ‘ Nat. Hist. Review,’ also Timbal-Lagrave in ‘ Bot 
July 1862, p. 238. With respect Zeitung,’ 1854, p. 772. 


Ouar. VILL. VIOLA. 319 


Viola nana.—Mr. Scott sent me seeds of this Indian 
species from the Sikkim Terai, from which I raised 
many plants, and from these other seedlings during 
several successive generations. They produced an 
abundance of cleistogamic flowers during the whole of 
each summer, but never a perfect one. When Mr. Scott 
wrote to me his plants in Calcutta were behaving simi- 
larly, though his collector saw the species in flower in 
its native site. This case is valuable as showing that 
we ought not to infer, as has sometimes been done, 
that a species does not bear perfect flowers when grow- 
ing naturally, because it produces only cleistogamic 
flowers under culture. The calyx of these flowers is 
sometimes formed of only three sepals; two being 
actually suppressed and not merely coherent with the 
others; this occurred with five out of thirty flowers 
which were examined for this purpose. The petals are 
represented by extremely minute scales. Of the sta- 
mens, two bear anthers which are in the same state as 
in the previous species, but, as far as I could judge, 
each of the two cells contained only from 20 to 25 de- 
licate transparent pollen-grains. These emitted their 
tubes in the usual manner. The three other stamens 
bore very minute rudimentary anthers, one of which 
was generally larger than the other two, but none of 
them contained any pollen. In one instance, however, 
a single cell of the larger rudimentary anther in- 
cluded a little pollen. The style consists of a short 
flattened tube, somewhat expanded at its upper end, 
and this forms an open channel leading into the 
ovarium, as described under V. canina. It is slightly 
bent towards the two fertile anthers. 

Viola Roxburghiana.—This species bore in my hot- 
house during two years a multitude of cleistogamic 
flowers, which resembled in all respects those of the 


320 CLEISTOGAMIC FLOWERS. Cuapr. VIII. 


last species ; but no perfect ones were produced. Mr. 
Scott informs me that in India it bears perfect flowers 
only during the cold season, and that these are quite 
fertile. During the hot, and more especially during 
the rainy season, it bears an abundance of cleisto- 
gamic flowers. 

Many other species, besides the five now described, 
produce cleistogamic flowers ; this is the case, accord- 
ing to D. Miller, Michalet, Von Mohl, and Hermann 
Miller, with V. elatior, lancifolia, sylvatica, palustris, 
mirabilis, bicolor, ionodium, and biflora. But V. tricolor 
does not produce them. 

Michalet asserts that V. palustris produces near 
Paris only perfect flowers, which are quite fertile; but 
that when the plant grows on mountains cleistogamic 
flowers are produced; and so it is with V. béflora. 
The same author states that he has seen in the case 
of V. alba flowers intermediate in structure between 
the perfect and cleistogamic ones. According to M. 
Boisduval, an Italian species, V. Ruppi, never bears 
in France “des fleurs bien apparentes, ce qui ne l’em- 
péche pas de fructifier.” 

It is interesting to observe the gradation in the 
abortion of the parts in the cleistogamic flowers of 
the several foregoing species. It appears from the 
statements by D. Miller and Von Mohl that in V. mi- 
rabilis the calyx does not remain quite closed ; all five 
stamens are provided with anthers, and some pollen- 
grains probably fall out of the cells on the stigma, 
instead of protruding their tubes whilst still enclosed, 
as in the other species. In V. hirta all five sta- 
mens are likewise antheriferous; the petals are not 
so much reduced and the pistil not so much modified 
as in the following species. In V. nana and elatior 
only two of the stamens properly bear anthers, but 


Cuapr. VILL. * OXALIS. 321 


sometimes one or even two of the others are thus pro- 
vided. Lastly, in V. canina never more than two of 
the stamens, as far as I have seen, bear anthers; the 
petals are much more reduced than in V. hirta, and 
according to D. Miller are sometimes quite absent. 
Oxalis acetosella—The existence of cleistogamic. 
flowers on this plant was discovered by Michalet.* 
They have been fully described by Von Mohl, and I 
ean add hardly anything to his description. In my 
specimens the anthers of the five longer stamens were 
nearly on a level with the stigmas; whilst the smaller 
and less plainly bilobed anthers of the five shorter 
stamens stood considerably below the stigmas, so that 
their tubes had to travel some way upwards. <Ac- 
cording to Michalet these latter anthers are some- 
times quite aborted. In one case the tubes, which 
ended in excessively fine points, were seen by me 
stretching upwards from the lower anthers towards 
‘the stigmas, which they had not as yet reached. My 
plants grew in pots, and long after the perfect flowers 
had withered they produced not only cleistogamic but 
a few minute open flowers, which were in an inter- 
mediate condition between the two kinds. In one of 
these the pollen-tubes from the lower anthers had 
reached the stigmas, though the flower was open. 
The footstalks of the cleistogamic flowers are much 
shorter than those of the perfect flowers, and are so 
much bowed downwards that they tend, according to 
Von Mohl, to bury themselves in the moss and dead 
leaves on the ground. Michalet also says that they 
are often hypogean. In order to ascertain the num- 
ber of seeds produced by these flowers, I marked eight 
of them; two failed, one cast its seed abroad, and the 


* “Bull. Soc. Bot. de France,’ tom. vii. 1860, p. 465. 


322 CLEISTOGAMIC FLOWERS. Cuap. VIII. 


remaining five contained on an average 10:0 seeds 
per capsule. This is rather above the average 9:2, 
which eleven capsules from perfect flowers fertilised 
with their own pollen yielded, and considerably. above - 
the average 7-9, from the capsules of perfect flowers 
fertilised with pollen from another plant; but this 
latter result must, I think, have been accidental. 
Hildebrand, whilst searching various Herbaria, ob- 
served that many other species of Oxalis besides O. 
acetosella produce cleistogamic flowers;* and I hear 
from him that this is the case with the heterostyled 
trimorphie O. incarnata from the Cape of Good Hope. 
Oxalis (Biophytum) sensitiva.—This plant is ranked 
by many botanists as a distinct genus, but as a sub- 
genus by Bentham and Hooker. Many of the early 
flowers on a mid-styled plant in my hot-house did not 
open properly, and were in an intermediate condition 
between cleistogamic and perfect. Their petals varied 
from a mere rudiment to about half their proper size ; 
nevertheless they produced capsules. I attributed 
their state to unfavourable conditions, for later in the 
season fully expanded flowers of the proper size ap- 
peared. But Mr. Thwaites afterwards sent me from 
Ceylon a number of long-styled, mid-styled, and short- 
styled flower-stalks preserved in spirits; and on the 
same stalks with the perfect flowers, some of which were 
fully expanded and others still in bud, there were 
small bud-like bodies containing mature pollen, but 
with their calyces closed. These cleistogamic flowers 
do not differ much in structure from the perfect ones 
of the corresponding form, with the exception that 
their petals are reduced to extremely minute, barely 
visible scales, which adhere firmly to the rounded 


* ‘Monatsbericht der Akad. der Wiss. zu Berlin,’ 1866, p. 369, 


Cuar. VIII. OXALIS. gue 


bases of the shorter stamens. Their ‘stigmas are much 
less papillose, and smaller in about the ratio of 13 to 
20 divisions of the micrometer, as measured trans- 
versely from apex to apex, than the stigmas of the 
perfect flowers. The styles are furrowed longitudinally, 
and are clothed with simple as well as glandular hairs, 
but only in the cleistogamic flowers produced by the 
long-styled and mid-styled forms. The anthers of the 
- longer stamens are a little smaller than the correspond- 
ing ones of the perfect flowers, in about the ratio of 
11 to 14. They dehisce properly, but do not appear 
to contain much pollen. Many pollen-grains were 
attached by short tubes to the stigmas; but many 
others, still adhering to the anthers, had emitted 
their tubes to a considerable length, without having 
come in contact with the stigmas. Living plants 
ought to be examined, as the stigmas, at least of the 
long-styled form, project beyond the calyx, and if 
visited by insects (which, however, is very improbable) 
might be fertilised with pollen from a perfect flower. 
The most singular fact about the present species is 
that long-styled cleistogamic flowers are produced by 
the long-styled plants, and mid-styled as well as 
short-styled cleistogamic flowers by the other two 
forms ; so that there are three kinds of cleistogamic 
and three kinds of perfect flowers produced by this 
one species! Most of the heterostyled species of 
Oxalis are more or less sterile, many absolutely so, if 
illegitimately fertilised with their own-form pollen. 
It is therefore probable that the pollen of the cleisto- 
gamic flowers has been modified in power, so as to act 
on their own stigmas, for they yield an abundance of 
seeds. We may perhaps account for the cleistogamic 
flowers consisting of the three forms, through the prin- 
ciple of correlated growth, by which the cleistogamie 


824 CLEISTOGAMIC FLOWERS. Cuap. VIII 


flowers of the double violet have been rendered 
double. 

Vandellia nummularifolia—Dr. Kuhn has collected* 
all the notices with respect to cleistogamic flowers in 
this genus, and has described from dried specimens 
those produced by an Abyssinian species. Mr. Scott 
sent me from Calcutta seeds of the above common 
Indian weed, from which many plants were success- 
ively raised during several years. The cleistogamic 
flowers are very small, being when fully mature under 
jy of an inch (1°27 mm.) in length. The calyx does 
not open, and within it the delicate transparent corolla 
remains closely folded over the ovarium. There are 
only two anthers instead of the normal number of four, 
and their filaments adhere to the corolla. The cells of 
the anthers diverge much at their lower ends and are 
only 7? of an inch (*181 mm.) in their longer diameter. 
They contain but few pollen-grains, and these emit 
their tubes whilst still within the anther. The pistil 
is very short, and is surmounted by a bilobed stigma. 
As the ovary grows the two anthers together with the 
shrivelled corolla, all attached by the dried pollen- 
tubes to the stigma, are torn off and carried upwards 
in the shape of a little cap. The perfect flowers gene- 
rally appear before the cleistogamic, but sometimes 
simultaneously with them. During one season a large 
number of plants produced no perfect flowers. It has 
been asserted that the latter never yield capsules; but 
this is a mistake, as they do so even when insects are 
excluded. Fifteen capsules from cleistogamic flowers 
on plants growing under favourable conditions con- 
tained on an average 64°2 seeds, with a maximum of 
87; whilst 20 capsules from plants growing much 


* ‘Bot. Zeitung,’ 1867, p. 65, 


Cuar. VIIL. ONONIS. S20 


crowded yielded an average of only 48. Sixteen cap- 
sules from perfect flowers artificially crossed with pollen 
from arother plant contained on an average 95 seeds, 
with a maximum of 137. Thirteen capsules from self- 
fertilised perfect flowers gave an average of 62 seeds, 
with a maximum of 135. Therefore the capsules from 
the cleistogamic flowers contained fewer seeds than 
those from perfect flowers when cross-fertilised, and 
slightly more than those from perfect flowers self- 
fertilised. 

Dr. Kuhn believes that the Abyssinian JV. sessiflora 
does not differ specifically from the foregoing species. 
But its cleistogamic flowers apparently include four 
anthers instead of two as above described. The plants, 
moreover, of V. sessiflora produce subterranean runners 
which yield capsules; and I never saw a trace of such 
runners in V. nummularifolia, although many plants 
were cultivated. 

Linaria spuria—Michalet says* that short, thin, 
twisted branches are developed from the buds in the 
axils of the lower leaves, and that these bury them- 
selves in the ground. They there produce flowers 
not offerimg any peculiarity in structure, excepting 
that their corollas, though properly coloured, are de- 
formed. These flowers may be ranked as cleistogamic, 
as they are developed, and not merely drawn, beneath 
the ground. 

Ononis columnx.—Plants were raised from seeds sent 
me from Northern Italy. The sepals of the cleisto- 
gamic flowers are elongated and closely pressed to- 
gether; the petals are much reduced in size, colour- 
ess, and folded over the interior organs. The fila- 
ments of the ten stamens are united into a tube, and 


* «Bull. Soc. Bot. de France,’ tom. vii. 1860, p, 468. 


326 CLEISTOGAMIC FLOWERS. _Cuap. VIII. 


this is not the case, according to Von Moll, with the 
cleistogamic flowers of other Leguminose. Five of 
the stamens are destitute of anthers, and alternate with 
the five thus provided. The two cells of the anthers 
are minute, rounded and separated from one another 
by connective tissue; they contain but few pollen- 
grains, and these have extremely delicate coats. The 
pistil is hook-shaped, with a plainly enlarged stigma, 
which is curled down, towards the anthers; it there- 
fore differs much from that of the perfect flower. 
During the year 1867 no perfect flowers were pro- 
duced, but in the following year there were both 
perfect and cleistogamic ones. 

Ononis minutissima.—My plants produced both per- 
fect and cleistogamic flowers ; but I did not examine 
the latter. Some of the former were crossed with 
pollen from a distinct plant, and six capsules thus ob- 
tained yielded on an average 3°66 seeds, with a maxi- 
mum of 5 in one. ‘Twelve perfect flowers were marked 
and allowed to fertilise themselves spontaneously under 
a net, and they yielded eight capsules, containing on 
an average 2°38 seeds, with a maximum of 3 in one. 
Fifty-three capsules produced by the cleistogamic 
flowers contained on an average 4:1 seeds, so that 
these were the most productive of all; and the seeds 
themselves looked finer even than those from the 
crossed perfect flowers. According to Mr. Bentham 
O. parviflora likewise bears cleistogamic flowers ; and 
he informs me that these flowers are produced by all 
three species early in the spring; whilst the perfect 
ones appear afterwards, and therefore in a reversed 
order compared with those of Viola and Oxalis. Some 
of the species, for instance Ononis columnex, bear a 
fresh crop of cleistogamic flowers in the autumn. 

Lathyrus nissolia apparently offers a case of the first 


Cuar. VIII. IMPATIENS. 327 


stage in the production of cleistogamic flowers, for on 
plants growing in a state of nature, many of the flowers 
never expand and yet produce fine pods. Some of 
the buds are so large that they seem on the point of 
expansion; others are much smaller, but none so small 
as the true cleistogamic flowers of the foregoing 
species. As I marked these buds with thread and 
examined them daily, there could be no mistake about 
their producing fruit without having expanded. 

Several other Leguminous genera produce cleisto- 
gamic flowers, as may be seen in the previous list; but 
much does not appear to be known about them. Von 
Mohl says that their petals are commonly rudimentary, 
that only a few of their anthers are developed, their 
filaments are not united into a tube and their pistils 
are hook-shaped. In three of the genera, namely Vicia, 
Amphicarpza, and Voandzeia, the cleistogamic flowers 
are produced on subterranean stems. The perfect 
flowers of Voandzeia, which is a cultivated plant, are 
said never to produce fruit ;* but we should remember 
how often fertility is affected by cultivation. 

Impatiens fulva.—Mr. A. W. Bennett has published 
an excellent description, with figures, of this plant.f 
He shows that the cleistogamic and perfect flowers 
differ in structure at a very early period of growth, so 
that the existence of the former cannot be due merely 
to the arrested development of the latter,—a conclusion 
which indeed follows from most of the previous de- 
scriptions. Mr. Bennett found on the banks of the Wey 
that the plants which bore cleistogamic flowers alone 
were to those bearing perfect flowers as 20 to 1; but 


* Correa de Mello (‘Journal African plant, which is sometimes 
Linn. Soc. Bot.’ yol. xi. 1870, p. cultivated in Brazil. 
254) particularly attended to the t ‘Journal Linn. Soc. Bot.’ vol 
flowering and fruiting of this xiii. 1872, p. 147. 


15 


328 CLEISTOGAMIC -FLOWERS. Cuar. VIII. 


we should remember that this is a naturalised species. 
The perfect flowers are usually barren in England ; but 
Prof. Asa Gray writes to me that after midsummer in 
the United States some or many of them: produce 
capsules. 

Impatiens neli-me-tangere.—I can add nothing of im- 
portance to Von Mohl’s description, excepting that 
one of the rudimentary petals shows a vestige of a 
nectary, as Mr. Bennett likewise found to be the ease 
with I. fulva. As in this latter species all five stamens 
produce some pollen, though small in amount; a 
single anther contains, according to Von Mohl, not 
more than 50 grains, and these emit their tubes 
while still enclosed within it. The pollen-grains of the 
perfect flowers are tied together by threads, but not, 
so as far as I could see, those of the cleistogamic 
flowers ; and a provision of this kind would here have 
been useless, as the grains can never be transported 
by insects. The flowers of I. balsamina are visited by 
humble-bees,* and I am almost sure that this is the 
case with the perfect flowers of I. noli-me-tangere. From 
the perfect flowers of this latter species covered with 
a net eleven spontaneously self-fertilised capsules were 
produced, and these yielded on an average 3°45 seeds. 
Some perfect flowers with their anthers still containing 
an abundance of pollen were fertilised with pollen from 
a distinct plant ; and the three capsules thus produced 
contained, to my surprise, only 2, 2, and 1 seed. As 
I. balsamina is proterandrous, so probably is the pre- 
sent species; and if so, cross-fertilisation was effected 
by me at too early a period, and this may account for 
the capsules yielding so few seeds. 

Drosera rotundifolia—The first flower-stems which 


* H. Miiller, ‘Die Befruchtung,’ &. p. 170 


Cuar. VIL. CLEISTOGAMIC FLOWERS. _. 329 


were thrown up by some plants in my green-house 
bore only cleistogamic flowers. The petals of small 
size remained permanently closed over the repro- 
ductive organs, but their white tips could just be 
seen between the almost completely closed sepals. 
The pollen, which was scanty in amount, but not so 
seanty as in Viola or Oxalis, remained enclosed 
within the anthers, whence the tubes proceeded and 
penetrated the stigma. As the ovarium swelled the 
little withered corolla was carried upwards in the 
form of a cap. These cleistogamic flowers produced 
an abundance of seed. Later in the season perfect 
flowers appeared. With plants in a state of nature the 
flowers open only in the early morning, as I have been 
informed by Mr. Wallis, who particularly attended to 
the time of their flowering. In the case of D. Anglica, 
the still folded petals on some plants in my green- 
house opened just sufficiently to leave a minute 
aperture; the anthers dehisced properly, but the 
pollen-grains adhered in a mass to them, and thence 
emitted their tubes, which penetrated the stigmas. 
These flowers, therefore, were in an intermediate con- 
dition, and could not be called either perfect or 
cleistogamic. 

A few miscellaneous observations may be added 
with respect to some other species, as throwing light 
on our subject. Mr. Scott states* that Hranthemum 
ambiguum bears three kinds of flowers,—large, con- 
spicuous, open ones, which are quite sterile,—others 
of intermediate size, which are open and moderately 
fertile—and lastly small closed or cleistogamic ones, 
which are perfectly fertile. Ruellia tuberosa, likewise 
one of the Acanthacez, produces both open and cleis- 


* «Journal of Botany, London, new series, vol. i. 1872, pp. 161-4. 


330 CLEISTOGAMIC FLOWERS. Omar. VILL. 


togamic flowers; the latter yield from 18 to 24, whilst 
the former only from 8 to 10 seeds ; these two kinds of 
flowers are produced simultaneously, whereas in several 
other members of the family the cleistogamic ones 
appear only during the hot season. According to 
‘Torrey and Gray, the North American species of He- 
lianthemum, when growing in poor soil, produce only 
cleistogamic flowers. The cleistogamic flowers of 
Specularia perfoliata are highly remarkable, as they 
are closed by a tympanum formed by the rudi- 
mentary corolla, and without any trace of an open- 
ing. The stamens vary from 3 to 5 in number, 
as do the sepals.* The collecting hairs on the pistil, 
which play so important a part in the fertilisation 
of the perfect flowers, are here quite absent. Drs. 
Hooker and Thomson statef that some of the Indian 
species of Campanula produce two kinds of flowers ; 
the smaller ones being borne on longer peduncles 
with differently formed sepals, and producing a more 
globose ovary. The flowers are closed by a tym- 
panum like that in Specularia. Some of the plants 
produce both kinds of flowers, others only one kind ; 
both yield an abundance of seeds. Professor Oliver 
adds that he has seen flowers on Campanula colorata 
in an intermediate condition between cleistogamic and 
perfect ones. 

The solitary almost sessile cleistogamic flowers pro- 
duced by Monochoria vaginalis are differently protected 
from those in any of the previous cases, namely, within 
“a short sack formed of the membranous spathe, 


* Von Mohl, ‘Bot. Zeitung, of the perfect flower is mostly 
1863, pp. 314 and 323. Dr. Brom- _5-cleft. 
field (‘ Phytologist,’ vol. iii. p. t+ ‘Journal Linn. Soe.’ vol. ii. 
530) also remarks that the calyx 1857, p. 7. See also Professor 
of the cleistogamic flowers is Oliver in ‘Nat. Hist. Review, 
usually only 3-cleft, while that 1862, p. 240. 


Cuar. VIL. CLEISTOGAMIC FLOWERS. 331 


without any opening or fissure.” There is only a 
single fertile stamen; the style is almost obsolete, 
with the three stigmatic surfaces directed to one side. 
Both the perfect and cleistogamic flowers produce 
seeds.* 

The cleistogamic flowers on some of the Mal- 
pighiaceze seem to be more profoundly modified than 
those in any of the foregoing genera. According to 
A. de Jussieuf they are differently situated from the 
perfect flowers; they contain only a single stamen, 
instead of 5 or 6; and it is a strange fact that this 
particular stamen is not developed in the perfect 
flowers of the same species. The style is absent or 
rudimentary ; and there are only two ovaries instead 
of three. Thus these degraded flowers, as Jussieu 
remarks, “laugh at our classifications, for the greater 
number of the characters proper to the species, to the 
genus, to the family, to the class disappear.” I may 
add that their calyces are not glandular, and as, 
according to Kerner,f the fluid secreted by such 
glands generally serves to protect the flowers from 
crawling insects, which steal the nectar without aiding 
in their cross-fertilisation, the deficiency of the glands 
in the cleistogamic flowers of these plants may perhaps 
be accounted for by their not requiring any such 
protection. 

As the Asclepiadous genus Stapelia is said to pro- 
duce cleistogamic flowers, the following case may be 
worth giving. I have never heard of the perfect flowers 
of Hoya carnosa setting seeds in this country, but some 
capsules were produced in Mr. Farrer’s hot-house ; 


* Dr. Kirk, ‘Journ. Linn. Soc. t ‘Die Schutzmittel der Bliithen 
vol. viii. 1864, p. 147. gegen unberufene Giste,’ 1876, 
t ‘Archives du Muséum,’ tom. p. 25. 
iii. 1843, pp. 35-38, 82-86, 589, 598. 


oon CLEISTOGAMIC FLOWERS. Cuay VII. 


and the gardener detected that they were the product 
of minute bud-like bodies, three or four of which 
could sometimes be found on the same umbel with the 
perfect flowers. They were quite closed and hardly 
thicker than their peduncles. The sepals presented 
nothing particular, but internally and alternating 
with them, there were five small flattened heart-shaped 
papille, like rudiments of petals ; but the homological 
nature of which appeared doubtful to Mr. Bentham 
and Dr. Hooker. No trace of anthers or of stamens 
could be detected ; and I knew from having examined 
many cleistogamic flowers what to look for. There 
were two ovaries, full of ovules, quite open at their 
upper ends, with their edges festooned, but with no 
trace of a proper stigma. In all these flowers one of 
the two ovaries withered and blackened long before 
the other. The one perfect capsule, 34 mches in 
length, which was sent me, had likewise been de- 
veloped from a single carpel. This capsule con- 
tained an abundance of plumose seeds, many of which 
appeared quite sound, but they did not germinate 
when sown at Kew. Therefore the little bud-like 
flower which produced this capsule probably was as 
destitute of pollen as were those which I examined. 
Juncus bufonius and Hordewm.—All the species 
hitherto mentioned which produce _ cleistogamic 
flowers are entomophilous ; but four genera, Juncus, 
Hordeum, Cryptostachys, and Leersia are anemophi- 
lous. Juncus bufonius is remarkable* by bearing in 
parts of Russia only cleistogamic flowers, which con- 
tain three instead of the six anthers found in the 
perfect flowers. In the genus Hordeum it has been 


* See Dr. Ascherson’s interesting paper in ‘ Bot. Zeitung,’ 1871, 
p- 5901, 


Cnap. VIII. LEERSIA. 333 


shown by Delpino* that the majority of the flowers are 
cleistogamic, some of the others expanding and ap- 
parently allowing of cross-fertilisation. I hear from 
Fritz Miller that there is a grass in Southern Brazil, 
in which the sheath of the uppermost leaf, half a 
metre in length, envelopes the whole panicle; and 
this sheath never opens until the self-fertilised seeds 
are ripe. On the roadside some plants had been cut 
down, whilst the cleistogamic panicles were develop- 
ing, and these plants afterwards produced free or un- 
enclosed panicles of small size, bearing perfect flowers. 

Leersia oryzoides—It has long been known that 
this plant produces cleistogamic flowers, but these were 
first described with care by M. Duval-Jouve.f I pro- 
cured plants from a stream near Reigate, and cultivated 
them for several years in my green-house. The cleis- 
togamic flowers are very small, and usually mature 
their seeds within the sheaths of the leaves. These 
flowers are said by Duval-Jouve to be filled by slightly 
viscid fluid; but this was not the case with several 
that I opened; but there was a thin film of fluid 
between the coats of the glumes, and when these were 
pressed the fluid moved about, giving a singularly 
deceptive appearance of the whole inside of the flower 
being thus filled. The stigma is very small and the 
filaments extremely short; the anthers are less than 
35 of an inch in length or about one-third of the 
Jeneth of those in the perfect flowers. One of the 
three anthers dehisces before the two others. Can 
this have any relation with the fact that in some other 


* ‘Bollettini del Comizio agra- on Hordeum, in ‘Monatsbericht d. 
rio Parmense.’ Marzo e Aprile, K.Akad. Berlin,’ Oct. 1872, p. 760, 
1871. An abstract of this valuable t+ ‘Bull. Bot. Soc. de France, 
paper is given in ‘ Bot. Zeitung,’ tom. x. 1863, p. 194. 

1871, p. 537. See also Hildebrand 


334 CLEISTOGAMIC FLOWERS. Cuar. VILL 


species of Leersia only two stamens are fully de- 
veloped ?* The anthers shed their pollen on the 
stigma; at least in one instance this was clearly the 
case, and by tearing open the anthers under water 
the grains were easily detached. ‘Towards the apex of 
the anther the grains are arranged in a single row and 
lower down in two or three rows, so that they could be 
counted ; and there were about 35 in each eell, or 70 
in the whole anther ; and this is an astonishingly small 
number for an anemophilous plant. The grains haye 
very delicate coats, are spherical and about 7,55 of 
an inch (‘0181 mm.), whilst those of the perfect flowers 
are about 75/55 Of an inch (‘0254 mm.) in diameter. 
M. Duval-Jouve states that the panicles very rarely 

protrude from their sheaths, but that when this does 
happen the flowers expand and exhibit well-developed 
ovaries and stigmas, together with full-sized anthers 
containing apparently sound pollen ; nevertheless such 
flowers are invariably quite sterile. Schreiber had pre- 
viously observed that if a panicle is only half protruded, 
this half is sterile, whilst the still included half is 
fertile. Some plants which grew in a large tub of 
water in my green-house behaved on one occasion in a 
very different manner. They protruded two very 
large much-branched panicles; but the florets never 
opened, though these included fully developed stig- 
mas, and stamens supported on long filaments with 
large anthers that dehisced properly. If these florets 
had opened for a short time unperceived by me and 
had then closed again, the empty anthers would 
have been left dangling outside. Nevertheless they 
yielded on August 17th an abundance of fine ripe 
seeds. Here then we have a near approach to the 


* Asa Gray, ‘Manual of Bot. of United States,’ 1896, p. 540. 


Cuap. VIII. LEERSIA. ooo 


single case as yet known* of this grass producing in a 
state of nature (in Germany) perfect flowers which 
yielded a copious supply of fruit. Seeds from the cleis- 
togamic flowers were sent by me to Mr. Scott in 
Calcutta, who there cultivated the plants in various 
ways, but they never produced perfect flowers. 

In Europe Leersia oryzoides is the sole representa- 
tive of its genus, and Duval-Jouve, after examining 
several exotic species, found that it apparently is the 
sole one which bears cleistogamic flowers. It ranges 
from Persia to North America, and specimens from 
Pennsylvania resembled the European ones in their 
concealed manner of fructification. There can there- 
fore be little doubt that this plant generally propa- 
gates itself throughout an immense area by cleisto- 
gamic seeds, and that it can hardly ever be invigorated 
by cross-fertilisation. It resembles in this respect 
those plants which are now widely spread, though they 
increase solely by asexual generation. 

Concluding Remarks on Cleistogamie Flowers—That 
these flowers owe their structure primarily to the 
arrested development of perfect ones, we may infer 
from such cases as that of the lower rudimentary petal 
in Viola being larger than the others, like the lower 
lip of the perfect flower,—from a vestige of a spur in 
the cleistogamic flowers of Impatiens,—from the ten 
stamens of Ononis being united into a tube,—and 
other such structures. The same inference may be 
drawn from the occurrence, in some instances, on the 
same plant of a series of gradations between the 
cleistogamic and perfect flowers. But that the former 
owe their origin ‘wholly to arrested development is 


* Dr. Ascherson, ‘ Bot. Zeitung” cases in my ‘Variation under 
1864, p. 350. Domestication, ch. xviii—2nd 
t I haye collected several such edit, vol. ii. p. 153. 


506 CONCLUDING REMARKS Cuar. VILL. 


by no means the case; for various parts have been 
specially modified, so as to aid in the self-fertilisation 
of the flowers, and as a protection to the pollen; for 
instance, the hook-shaped pistil in Viola and in some 
other genera, by which the stigma is brought close 
to the fertile anthers,—the rudimentary corolla of 
Specularia modified into a perfectly closed tympanum, 
and the sheath of Monochoria modified into a closed 
sack,—the excessively thin coats of the pollen-grains, 
—the anthers not being all equally aborted, and other 
such cases. Moreover Mr. Bennett has shown that 
the buds of the cleistogamic and perfect flowers of 
{mpatiens differ at a very early period of growth. 

The degree to which many of the most important 
organs in these degraded flowers have been reduced 
or even wholly obliterated, is one of their most re- 
markable peculiarities, reminding us of many parasitic 
animals. In some cases only a single anther is left, 
and this contains but few pollen-grains of diminished 
size; in other cases the stigma has disappeared, 
leaving a simple open passage into the ovarium. It 
is also interesting to note the complete loss of trifling 
points in the structure or functions of certain parts, 
which though of service to the perfect flowers, are of 
none to the cleistogamic; for instance the collecting 
hairs on the pistil of Specularia, the glands on the 
calyx of the Malpighiacew, the nectar-secreting ap- 
pendages to the lower stamens of Viola, the secretion 
of nectar by other parts, the emission of a sweet odour, 
and apparently the elasticity of the valves in the 
buried capsules of Viola odorata. We here see, as 
throughout nature, that as soon as any part or 
character becomes superfluous it tends sooner or later 
to disappear. 

Another peculiarity in these flowers is that the 


Cuar. VI. ON CLEISTOGAMIC FLOWERS. 337 
pollen-grains generally emit their tubes whilst still 
enclosed within the anthers; but this is not so re- 
markable a fact as was formerly thought, when the 
ease of Asclepias was alone known.* It is, however, 
a wonderful sight to behold the tubes directing them- 
selves in a straight line to the stigma, when this 
is at some little distance from the anthers. As 
soon as they reach the stigma or the open passage 
leading into the ovarium, no doubt they penetrate it, 
guided by the same means, whatever these may be, 
as in the case of ordinary flowers. I thought that 
they might be guided by the avoidance of light: some 
pollen-grains of a willow were therefore immersed in 
an extremely weak solution of honey, and the vessel 
was placed so that the light entered only in one di- 
rectign, laterally or from below or from above, but the 
long tubes were in each case protruded in every 
possible direction. 

As cleistogamic flowers are completely closed they 
are necessarily self-fertilised, not to mention the 
absence of any attraction to insects; and they thus 
differ widely from the great majority of ordinary 
flowers. Delpino believesf that cleistogamiec flowers 
have been developed in order to ensure the production 
of seeds: under climatic or other conditions which tend 


* The case of Asclepias was de- 
seribed by R. Brown. Baillon as- 
serts (‘ Adansonia,’ tom. ii. 1862, 
p. 58) that with many plants the 
tubes are emitted from pollen- 
grains which have not come into 
contact with the stigma; and that 
they may be seen advancing hori- 
zontally through the air towards 
the stigma. I have observed the 


emission of the tubes from the 


pollen-masses whilst still within 
the anthers, in three widely distinct 
Orchidean genera. namely Aceras, 
Malaxis, and Neottia: see ‘The 
Various Contrivances by which 
Orchids are Fertilised,’ 2nd edit. 
p. 258. 

t ‘Sull’ Opera la Distribuzione 
dei Sessi nelle Piante,’ 1867, 
p. 30. 


338 CONCLUDING REMARKS Cuar. VIIL 


to prevent the fertilisation of the perfect flowers. I do 
not doubt that this holds good to a certain limited extent, 
but the production of a large supply of seeds with little 
consumption of nutrient matter or expenditure of vital 
force is probably a far more efficient motive power. 
The whole flower is much reduced in size; but what 
is much more important, an extremely small quantity 
of pollen has to be formed, as none is lost through the 
action of insects or the weather; and pollen contains 
much nitrogen and-phosphorus. Yon Mohl estimated 
that a single cleistogamic anther-cell of Ozxalis aceto- 
sella contained from one to two dozen pollen-grains ; 
we will say 20, and if so the whole flower can have 
produced at most 400 grains; with Impatiens the 
whole number may be estimated. in the same manner 
at 250; with Leersia at 210; and with Vzola nana at 
only 100. These figures are wonderfully low com- 
pared with the 248,600 pollen-grains produced by a 
flower of Leontodon, the 4,863 by an Hibiscus, or the 
3,654,000 by a Peony.* We thus see that cleisto- 
gamic flowers produce seeds with a wonderfully small 
expenditure of pollen; and they produce as a general 
rule quite as many seeds as the perfect flowers. 

That the production of a large number of seeds is 
necessary or beneficial to many plants needs no eyi- 
dence. So of course is their preservation before they 
are ready for germination ; and it is one of the many 
remarkable peculiarities of the plants which bear 
cleistogamic flowers, that an incomparably larger pro- 
portion of them than of ordinary plants bury their 
young ovaries in the ground;—an action which it 
may be presumed serves to protect them from being 


* The authorities for these statements are given in my ‘ Effects of 
Cross and Self-Fertilisation,’ p. 376. 


Cuar. VIII. ON CLEISTOGAMIC FLOWERS. 309 


devoured by birds or other enemies. But this advan- 
tage is accompanied by the loss of the power of wide 
dissemination. No less than eight of the genera 
in the. list at the beginning of this chapter include 
species which act in this manner, namely, several 
kinds of Viola, Oxalis, Vandellia, Linaria, Commelina, 
and at least three genera of Leguminosee. The seeds 
also of Leersia, though not buried, are concealed in 
the most perfect manner within the sheaths of the 
leaves. Cleistogamic flowers possess great facilities 
for burying their young ovaries or capsules, owing to 
their small size, pointed shape, closed condition and 
the absence of a corolla; and we can thus understand 
how it is that so many of them have acquired this 
curious habit. 

It has already been shown that in about 32 out of 
the 55 genera in the list just referred to, the perfect 
flowers are irregular; and this implies that they have 
been specially adapted for fertilisation by insects. 
Moreover three of the genera with regular flowers are 
adapted by other means for the same end. Flowers 
thus constructed are liable during certain seasons to 
be imperfectly fertilised, namely, when the proper 
insects are scarce; and it is difficult to avoid the 
belief that the production of cleistogamic flowers, 
which ensures under all circumstances a full supply 
of seed, has been in part determined by the perfect 
flowers being liable to fail in their fertilisation. But 
if this determining cause be a real one, it must be of 
subordinate importance, as four of the genera in the 
list are fertilised by the wind; and there seems no 
reason why their perfect flowers should fail to be 
fertilised more frequently than those in any other 
anemophilous genus: In contrast with what we here 
see with respect to the large proportion of the perfect 


J40 CONCLUDING REMARKS Ouar. VIIL. 
flowers being irregular, one genus alone out of the 38 
heterostyled genera described in the previous chapters 
bears such flowers; yet all these genera are absolutely 
dependent on insects for their legitimate fertilisation. 
I know not how to account for this difference in the 
proportion of the plants bearing regular and irregular 
flowers in the two classes, unless it be that the hetero- 
styled flowers are already so well adapted for cross-fer- 
tilisation, through the position of their stamens and 
pistils and the difference in power of their two or 
three kinds of pollen, that any additional adaptation, 
namely, through the flowers being made irregular, 
has been rendered superfluous. 

Although cleistogamic flowers never fail to yield 
a large number of seeds, yet the plants bearing them 
usually produce perfect flowers, either simultaneously 
or more commonly at a different period; and these 
are adapted for or admit of cross-fertilisation. From 
the cases given of the two Indian species of Viola, 
which produced in this country during several years 
only cleistogamic flowers, and of the numerous plants 
of Vandellia and of some plants of Ononis which 
behaved during one whole season in the same manner, 
it appears rash to infer from such cases as that of 
Salvia clestogama not haying produced perfect flowers 
during five years in Germany,* and of an Aspicarpa 
not having done so during several years in Paris, that 
these plants would not bear perfect flowers in their 
native homes. Von Mohl and several other botanists 
have repeatedly insisted that as a general rule the 
perfect flowers produced by cleistogamic plants are 
sterile; but it has been shown under the head of the 
several species that this is not the case. The perfect 


* Dr. Ascherson, ‘ Bot. Zeit.’ 1871, p. 556. 


Cuar. VILL. ON CLEISTOGAMIC FLOWERS. 341 


flowers of Viola are indeed sterile unless they are 
visited by bees; but when thus visited they yield the 
full number of seeds. As far as I have been able to 
discover there is only one absolute exception to the 
rule that the perfect flowers are fertile, namely, that 
of Voandzeia; and in this case we should remember 
that cultivation often affects injuriously the repro- 
ductive organs. Although the perfect flowers of 
Leersia sometimes yield seeds, yet this occurs so 
rarely, as far as hitherto observed, that it practically 
forms a second exception to the rule. 

As cleistogamic flowers are invariably fertilised, and 
as they are produced in large numbers, they yield 
altogether a much larger supply of seeds than do 
the perfect flowers on the same plant. But the latter 
flowers will occasionally be cross-fertilised, and their 
offspring will thus be invigorated, as we may infer 
from a wide-spread analogy. But of such invigoration 
I have only a small amount of direct evidence: two 
crossed seedlings of Ononis minutissima were put into 
competition with two seedlings raised from cleisto- 
gamic flowers ; they were at first all of equal height ; 
the crossed were then slightly beaten; but on the fol- 
lowing year they showed the usual superiority of their 
class, and were to the self-fertilised plants of cleisto- 
gamic origin as 100 to 88 in mean height. With 
Vandellia twenty crossed plants exceeded in height 
twenty plants raised from cleistogamic seeds only by 
a little, namely, in the ratio of 100 to 94. 

It is a natural inquiry how so many plants belong- 
ing to various very distinct families first came to have 
the development of their flowers arrested, so as ulti- 
mately to become cleistogamic. That a passage from 
the one state to the other is far from difficult is shown 
by the many recorded cases of gradations between the 


342 CONCLUDING REMARKS Cuap. VIII. 


two states on the same plant, in Viola, Oxalis, Biophy- 
tum, Campanula, &e. In the several species of Viola 
the various parts of the flowers have also been modified 
in very different degrees. Those plants which in their 
own country produce flowers of full or nearly full size, 
but never expand (as with Thelymitra), and yet set 
fruit, might easily be rendered cleistogamic. Lathyrus 
nissolia seems to be in an incipient transitional state, 
as does Drosera Anglica, the flowers of which are not 
perfectly closed. There is good evidence that flowers 
sometimes fail to expand and are somewhat reduced 
‘in size, owing to exposure to unfavourable conditions, 
but still retain their fertility unimpaired. Linnzeus 
observed in 1753 that the flowers on several plants 
brought from Spain and grown at Upsala did not 
show any corolla and yet produced seeds. Asa 
Gray has seen flowers on exotic plants in the North- 
ern United States which never expanded and yet 
fruited. With certain English plants, which bear 
flowers during nearly the whole year, Mr. Bennett 
found that those produced during the winter season 
were fertilised in the bud; whilst with other species 
having fixed times for flowering, but “which had 
been tempted by a mild January to put forth a few 
wretched flowers,” no pollen was discharged from the 
anthers, and no seed was formed. The flowers of 
Lysimachia vulgaris if fully exposed to the sun expand 
properly, while those growing in shady ditches have 
smaller corollas which open only slightly ; and these 
two forms graduate into one another in intermediate 
stations. Herr Bouché’s observations are of especial 
interest, for he shows that both temperature and the 
amount of light affect the size of the corolla; and he 
gives measurements proving that with some plants 
the corolla is diminished by the increasing cold and 


Cuap. VIII. ON CLEISTOGAMIC FLOWERS. 343 


darkness of the changing season, whilst with others 
it is diminished by the increasing heat and light.* 
The belief that the first step towards flowers being 
rendered cleistogamic was due to the conditions to 
which they were exposed, is supported by the fact 
of yarious plants belonging to this class either not pro- 
ducing their cleistogamic flowers under certain condi- 
tions, or, on the other hand, producing them to the 
complete exclusion’ of the. perfect ones. Thus some 
species of Viola do not bear cleistogamic flowers when 
growing on the lowlands or in certain districts. Other. 
plants when cultivated have failed to produce perfect 
flowers during several successive years; and this is 
the case with Juncus bufonius in its native land of 
Russia. Cleistogamic flowers are produced by some 
species late and by others early in the season ; and this 
agrees with the view that the first step towards their de- 
velopment was due to climate; though the periods at 
which the two sorts of flowers now appear must. since 
have become much more distinctly defined. We do not 
know whether too low or too high a temperature or the 
amount of light acts in a direct manner on the size of 
the corolla, or indirectly through the male organs being 
first affected. However this may be, if a plant were 
prevented either early or late in the season from fully 
expanding its corolla, with some reduction in its size, 
but with no loss of the power of self-fertilisation, then 
natural selection might well complete the work and 


* For the statement by Linnzeus, 
see Mobl in ‘ Bot. Zeitung,’ 1863, 
p. 327. Asa Gray, ‘ American 
Journal of Science,’ 2nd _ series, 
vol. xxxix. 1865, p.105. Bennett 
in ‘ Nature,’ Nov. 1869, p. 11. 
The Rey. G. Henslow also says 
(‘ Gardener’s Chronicle,’ 1877, p. 
271: also ‘ Nature,’ Oct. 19, 1876, 


p- 543) “that when the autumn 
draws on, and habitually in winter 
for such of our wild flowers as 
blossom at that season,” the flowers 
are self-fertilised. On Lysima- 
chia, H. Miiller, ‘ Nature” Sept. 
1873, p. 433. Bouche, ‘ Sitzungs- 
bericht der Gesell. Naturforsch, 
Freunde’ Oct. 1874, p. 90. 


344 GENERAL CONCLUSIONS. Cuar. VIII. 


render it strictly cleistogamic. The various organs 
would also, it is probable, be modified by the peculiar 
conditions to which they are subjected within a com- 
pletely closed flower; also by the principle of corre- 
lated growth, and by the tendency in all reduced 
organs finally to disappear. The result would be the 
production of cleistogamic flowers such as we now 
see them; and these are admirably fitted to yield a 
copious supply of seed at a wonderfully small cost to 
the plant. 


I will now sum up very briefly the chief conclusions 
which seem to follow from the observations given in 
this volume. Cleistogamic flowers afford, as just 
stated, an abundant supply of seeds with little ex- 
penditure ; and we can hardly doubt that they have 
had their structure modified and degraded for this 
special purpose; perfect flowers being still almost al- 
ways produced so as to allow of occasional cross-fertilisa- 
tion. Hermaphrodite plants have often been rendered 
-‘moncecious, dicecious or polygamous ; but as the sepa- 
ration of the sexes would have been injurious, had not 
pollen been already transported habitually by in- 
sects or by the wind from flower to flower, we may 
assume that the process of separation did not com- 
mence and was not completed for the sake of the 
advantages to be gained from cross-fertilisation. The 
sole motive for the separation of the sexes which 
occurs to me, is that the production of a great number 
of seeds might become superfluous to a plant under 
changed conditions of life ; and it might then be highly 
beneficial to it that the same flower or the same indi- 
vidual should not have its vital powers taxed, under 
the struggle for life to which all organisms are sub- 
jected, by producing both pollen and seeds. With 


Cuap. VILL. GENERAL CONCLUSIONS. 345 


respect to the plants belonging to the gyno-diceciogis 
sub-class, or those which co-exist as hermaphrodites 
and females, it has been proved that they yield a 
much larger supply of seed than they would have 
done if they had all remained hermaphrodites; and we 
may feel sure from the large number of seeds pro- 
duced by many plants that such production is often 
necessary or advantageous. It is therefore probable 
that the two forms in this sub-class have been sepa- 
rated or developed for this special end. 

Various hermaphrodite plants have become hetero- 
styled, and now exist under two or three forms; and 
we may confidently believe that this has been effected 
in order that cross-fertilisation should be assured. 
For the full and legitimate fertilisation of these plants 
pollen from the one form must be applied to the 
stigma of another. If the sexual elements belonging 
to the same form are united the union is an illegiti- 
mate one and more or less sterile. With dimorphic 
species two illegitimate unions, and with trimorphic 
species twelve are possible. There is reason to believe 
that the sterility of these unions has not been specially 
acquired, but follows as an incidental result from the 
sexual elements of the two or three forms having been 
adapted to act on one another in a particular manner, 
so that any other kind of union is inefficient, like 
that between distinct species. Another and still more 
remarkable incidental result is that .the seedlings 
from an illegitimate union are often dwarfed and 
more or less or completely barren, like hybrids from 
the union of two widely distinct species. 


( 346 ) 


INDEX. 


ACANTHACEZ, 


A. 


Acanthacex, 313 

Acer campestre, 12, 308 

Adoxa, 9 

Myiphila elata, 123 

mollis, 123 

obdurata, 124, 286 

Alefeld, Dr., on Linum, 100 

Alisma natans, 311 

Amphicarpxa, 327 

Amsinckia spectabilis, 110; varia- 
bility in length of stamens and 
pistil, 261, 266 

Anchusa arvensis, 111 

Androsace vitalliana, 53 

Anthers, size of, in different forms, 
252; contabescent, 283 

Arachis, 312 

Arnebia hispidissima, 111 

Ascherson, Dr., on Salvia cleisto- 
gama, 313, 340; Juncus bufonius, 
332; Leersia oryzoides, 335 

Asclepias, 337 

Ash, the common, 11 

Asperula scoparia, 285 

Axell on Primula stricta, 50 


B. 


Babington, Prof.,on Primula elatior, 
72; Stellaria graminea, 313 

3aillon, emission of the tubes from 
pollen-grains, 337 

Belhomme, M., on ray-florets, 6 

Bennett, A. W., on Impatiens fulva, 
327; flowers fertilised whilst in 
the bud state, 342 

Bentham, Mr., on the differentiation 
of the sexes, 11 


COROLLA. 


Bentham, Mr., on the cleistogamic 
flowers of Ononis, 326 

Boraginex, 101 

Boreau on cowslip and primrose, 57 

Borreria, 127 

Bouché on Pavonia, 313; effect of 
temperature and light on corolla, 
342 

Bouvardia leiantha, 135 

Braun on Dracocephalum, 299 

Breitenbach, W., on Primula elatior, 
34, 272 

Bromfield, Dr., on primrose and 
cowslip, 57; Primula elatior, 73 ; 
Specularia perfoliata, 330 

Brown, Robert, on sexual changes, 
282 

Buckwheat, the common, 111 


C, 


Caltha palustris, 13 

Campanula colorata, 330 

Cardamine amara, 307 

Caspary, Prof., on Rhamnus cathar- 
ticus, 294 

Cattleya, 313 

Chamissoa, 292 

Cinchona micrantha, 134 

Cleistogamic flowers, 310; list of 
genera, 312; on their origin, 343 

Cnicus acaulis, 307 

palustris, 307 

Coccocypselum, 133; pollen-grains 
of, 250 

Coprosma, 285 

Cordia, 117; pistil of, 253 

Corolla, difference in size in the 
sexes of the same species, 307- 
309 


INDEX. 


347 


CORYDALIS. 


Corydalis, 146 

Corylus avellana, 10 

Cowslip, the common, 14; short- 
and long-styled, 19-22, 56-71 

Cratoxylon formosum, 123 

Crocker, C. W., on Plantago lanceo- 
lata, 306 

Cryptostachys, 313, 332 

Cuphea purpurea, 168 


D. 


Darwin, Charles, on reproductive 
organs under cultivation, 7; in- 
tercrossed plants, 30; prepotency 
of pollen, 62; insects fertilising 
flowers, 79; Cephalanthera gran- 
diflora, 98; Epidendron and Cat- 
tleya, 313; number of pollen- 
grains, 338 

, W., on Pulmonaria angusti- 
folia, 105, 107 

Datura arborea, 251 

Delpino, plants fertilised by the 
wind, 10; on the walnut, 10; 
Polygonacex, 114; pollen-grains, 
250; Thymus serpyllum, 299; 
elused or cleistogamic flowers, 
311, 337; Viola odorata, 317 

Dianthus barbatus, 30 

Dickie, Dr., on Eriophorum angusti- 
folium, 307 

Dictamuus fraxinella, 146 

Diodia, 135 

Dicecious and sub-dicecious plants, 
287 

Discospermum, 286 

Doubleday, H., on Primula elatior, 
13 

Dracocephalum Moldavicum, 299 

Drosera Anglica, 329, 342 

rotundifolia, 328 

Duval-Jouve, M., on Cryptostachys, 
313; Leersia oryzoides, 333, 334 

Dyer, Thiselton, on Salvia Hor- 
minum, 8; Cratoxylon formosum, 
123 


E. 


Echium vulgare, 111, 305, 307 
Epidendron, 313. 


GRAY. 


Epigza repens, 297 

Eranthemum ambiquum, 329 

Eriophorum angustifolium, 307 

Erythroxylum, 121; pollen-grains of, 
250 

Buonymus Buropxus, 287-293 

Euphrasia officinalis, 4 

Euryale, 311 


F. 


Faramea, 128; pollen-grains of, 129 

Fitzgerald, Mr., on Thelymitra, 313 

Forsythia suspensa, 117; stamens, 
252 

viridissima, 117 

Fragaria Chiloensis, 293 

elatior, 293 

—— vesca, 293 

Virginiana, 293 

Fraxinus excelsior, 11 


G. 


Galium cruciatum, 286 

Gartner on the sterility of unions 
between distinct species, 29; Pri- 
mula vulgaris and veris, 58, 59; 
hybrid Verbascwms, 76, 77, 80; 
prepotency of pollen, 241; varia- 
tion in the sexual powers of 
plants, 267 ; contabescent anthers, 
193, 283 

Gentianex, 115 

Geraniacex, 169 

Geranium sylvaticum, 308 

Gesneria pendulina, 261 

Gilia aggregata, 118 

coronopifolia, 119 

— micrantha, 119 

—— nudicaulis, 419 

—— pulchella, 118 

Gillibert on Menyanthes, 311 

Gloriosa Lily, the, 146 

Godron on hybrid Primulas, 55 

Gray, Prof, Asa, proposes the term 
heterogone or heterogonous, 2; on 
Linum, 101; Leucosmia Bur- 
nettiana and acuminata, 114; 
Forsythia suspensa, 117; Gilia 
pulchella, 118; G. coronopifolia, 


348 


GYNO-DIGCIOUS, 


119; Phlox subulata, 119; Mit- 
chella repens, 125; heterostyled 
plants, 244; Coprosma, 285; Hu- 
onymus, 287; Rhamnus lanceo- 
latus, 295, 296; Epigzwa repens, 
297; Ilex opaca, 298; Plantago 
media, 307; Oxybaphus and Nycta- 
ginia, 313; Impatiens fulva, 328 ; 
Leersia, 334; cleistogamic flowers, 
342 
Gyno-dicecious plants, 298 


H. 


Hart, Mr., on Nepeta glechoma, 301 

Hautbois Strawberry, the, 293 

Hedyotis, 133 

Henslow, Rey. Prof., on hybrid Pri- 
mule, 61 

Henslow, Rev. G., on flowers self- 
fertilised during the winter, 343 

Herbert, Dr., on hybrid Primulz, 
61 

Heterostyled plants, illegitimate off- 
spring of, 188-243; essential cha- 
racter of, 244; summary of the 
differences of fertility between 
legttimately and illegitimately fer- 
tilised plants, 246; diameter of 
pollen-grains, 249 ; size of anthers, 
structure of stigma, 252; list of 
genera, 255; advantages derived 
from Heterostylism, 258; means 
by which plants became hetero- 
styled, 260 ; transmission of form, 
268; equal-styled varieties, 272; 
final remarks, 275 

— dimorphic plants, 14-54, S1- 
136 

— trimorphic plants, 187-187 

Fibiscus, pollen-grains, 338 

Hildebrand, Prof., introduces the 
word “ heterostyled,” 2; on the 
ray-florets of the Composite, 5, 6; 
Primula Sinensis, 38, 40-438, 192, 
217; Linwn grandiflorum, 86, 87 ; 
L. perenne, 92; Pulmonaria offi- 
cinalis, 101-108, 107, 239; P. 
azurea, 110; Polygonum fagopy- 
rum, 111; Ozxalis, 169, 171-174, 
178, 182, 211-213, 322; herma- 


INDEX. 


KERNER, 


phrodite plants becoming uni- 
sexual, 283; Hordewm, 333 

Homostyled species of Primula, 49 

Hooker, Dr., on Campanula, 330 

Hordeum, 332 

Hottonia inflata, 53, 313 

palustris, 50; relative fertility, 
52; anthers of, 252; papille on 
stigma, 254 

Houstonia cerulea, 132, 254 

Hoya carnosa, 331 

Hybrid Primulas, 55-71 

Hydrangea, 6, 7 

Hypericinex, 123 

Hyssopus officinalis, 299 


| 


Llex aquifolium, 297 

opaca, 298 

Illegitimate offspring of heterostyled 
plants, 188; Lythrum salicaria, 
dwarfed stature and sterility, 192 ; 
Oxalis, transmission of form to 
seedlings, 212; Primula Sinensis, 
in some degree dwarfed, 215; 
equal-styled varieties, 218-223 ;- 
Primula vulgaris, 224;  trans- 
mission of form and colour, 225; 
seedlings, 227; P. vweris, 228; 
dwarfed stature and _ sterility, 
229-234; equal-styled varieties, 
234, 238; parallelism between 
illegitimate fertilisation and hy-« 
bridism, 242 

Illecebrum, 311 

Impatiens, pollen-grains of, 338 

balsamina, 328 

—— fulva, 327 

noli-me-tangere, 328 


J. 


Juglans regia, 10 
Juncus bufonius, 332, 343 
Jussieu, A. de, on Malpighiacex, 
331 
K, 


Kerner, Prof., on ray-florets, 6 ; Auri- 
cula, 43 ; hybrid forms of Primula, 
55, 73; on use of hairs within 


INDEX. 


J49 


KIRK. 


the corolla, 128; size of corolla in 


male flowers, 309; use of glands 


as a protection to flowers, 331 

Kirk, Dr., on Monochoria vaginalis, 
331 

Knozxia, 135 

Koch on Primula longiflora, 50 

Krascheninikowia, 312 

Kuhn, Dr., on cleistogamic flowers, 
3, 310, 311; list of plants pro- 
ducing differently formed seeds, 
9; heterostyled plants, 244; Van- 
dellia nummularifolia, 324; V. 
sessifloru, 325 


L. 


Lagerstremia Indica, 167 ' 

parviflora, 168 

regine, 168 

Lathyrus nissolia, 326, 342 

Lecoq, H., on the common maple, 
12; cowslips and primroses, 57 ; 
Primula elatior, 72; Linum Aus- 
triacum, 98; Lythrum hyssopi- 
folia, 166; Rhamnus, 296; gyno- 
dicecious plants, 299; Scabiosa 
succisa, 309 ; Viola odorata, 317 

Leersia oryzoides, 333-335 ; pollen- 
grains of, 338 

Leggett, Mr., Pontederia cordata, 
187 

Legitimate unions, summary on the 
fertility of the two, compared with 
that of the two illegitimate in Pri- 
mula, 46-49; fertility of, com- 
pared with illegitimate, 246 

Leighton, Rev. W. A., on the cow- 
slip and primrose, 56; Verbascum 
virgatum, 78 

Leontodon, pollen-grains, 338 

Leptosiphon, 119 

Leucosmia acuminata, 114 


Lily, the Gloriosa, 146 


Burnettiana, 114; stigma, 253 


Limnanthemum Indicum, 116; pol- | 


len-grains, 250; anthers, 252 
Linaria spuria, 325 
Lindley on Fragaria elatior, 293 
Linnzus on Primula veris, vulgaris, 
and elatior, 56 
Linum angustifolium. 100 


MENYANTHES, 


Linum Austriacum, 97 

catharticum, 100 

corymbiferum, 100 

Jlavum, 81, 98; stamens, 252 

grandiflorum, 81; various ex- 

periments, 87-89, 96; pistils and 

stamens, 253, 254; sterile with its 

own-form pollen, 264, 266 

Lewisii, 101 

perenne, 90; torsion of the 

styles, 95; long-styled form, 97; 

stigma, 247 

salsoloides, 109 

trigynum, 100 

usitatissimum, 100 

Lipostoma, 134 

Lysimachia vulgaris, 4, 342 

Lythrum Grefferi, 165 

hyssoptfolia, 166 

salicaria, 116, 137; power of 
mutual fertilisation between the 
three forms, 149-157; summary 
of results, 157-165; illegitimate 
offspring from the three forms, 
191-203 ; concluding remarks on, 
203-211; mid-styled form, 241, 
257, 258, 280; seeds, 248 

—— thymifolia, 165 


M. 


Malpighiacex, 331 

Manettia bicolor, 135 

Maple, the common, 12 

Marshall, W., on Primula elatior, 
73; Plantago lanceolata, 306 

Masters, Dr. Maxwell, on cleisto- 
gamic flowers, 3 

Maximowicz on Krascheninikowia, 
312 

Meehan, Mr., on Mitchella, 285 ; 
Epigza repens, 297 

Melissa clinipodium, 299 

officinalis, 299 

Mello, Correa de, on Arachis, 
Voandzeia, 327 

Mentha aquatica, 299 

hirsuta, 298 

vulgaris, 298 

Menyanthes, 311 

trifoliata, 115 


312; 


390 


INDEX. 


MICHALET, 


Michalet on Oxalis acetosella, 321 ; 
Linaria spuria, 325 

Mitchella, 285 

repens, 125 

Mohl, H. von, on the common 
cowslip, 14; size of corolla in the 
sexes of the same species, 307, 
308; Trifolium and Arachis, 312 ; 
cleistogamie flowers, 314, 342; 
Oxalis acetosella, 321; Impatiens 
noli-me-tangere, 320; Specularia 
perfoliata, 330 

Mollia lepidota, 168 

speciosa, 168 

Monnier, M., on Viola, 318 

Monochoria vaginalis, 330 

Mulberry, the, 10 

Miiller, D., on Viola canina, 314 

Miiller, Fritz, on pollen of the Vil- 
larsia, 116; Faramea, 128-130; 
Posoqueria fragrans, 131; Nesxa, 
167; Ozxalis, 180, 181; Pontederia, 
183-185; Oxalis Regnelli, 212; 
Chamissoa, 292 

Miiller, H., on the frequency of 
visits by insects to the Umbelli- 
fere and Composite, 5; on dicho- 
gamy, 10; on Anthophora and 
Bombylius sucking the cowslip, 
22; Primula elatior, 32 ; P. villosa, 
49; Hottonia palustris, 51; table 
of relative fertility of, 52, 53; 
Linum catharticum, 100; Poly- 
gonum fagopyrum, 113; Lythrum 
salicaria, 145; on the origin of 
heterostylism, 263; on the La- 
biatex, 299, 304; Thymus serpyllum, 
300; Scabiosa arvensis, 305; Plan- 
tago lanceolata, 306; size of co- 
rolla in the two sexes of the same 
species, 308; Impatiens balsa- 
mina, 328; Lysimachia, 343 

Myosotis, 308 


N. 


Nepeta glechoma, 301 

Nertera, 285 

Nesexa verticillata, 167 

Nolana jprostrata, variability in 
length of stamens and pistil, 261 

Nyctaginia, 313 


POLEMONIACEZR, 


0. 


Oldenlandia, 132 

Oleacex, 117 

Oliver, Prof., on ovules of Primula 
veris, 17; Viola, 318; Campanula 
colorata, 330 

Ononis columnex, 325 

minutissima, 326, 341 

parviflora, 326 

Origanum vulgare, 298 

Ozxalis acetosella, 181, 182 ; pistil of, 
261; cleistogamic flowcrs, 321; 
pollen-grains, 338 

—— Bowii, 179 

compressa, 179 

corniculata, 181 

—— Deppei, 179 

hedysaroides, 213 

homostyled species, 181 

incarnata, 322 

Regnelli, 173-175, 212 

rosea, 178, 213 

—— (Biophytum)  sensitiva, 
322; stigma, 253 

speciosa, 169, 175, 212 

stricta, 181, 182 

tropxoloides, 182 

—— Valdiviana, 170-172, 211, 212 

Oxlip, the Bardwell, 32, 72 . 

——, the common, 55; differences 
in structure and function between 
the two parent-species, 56 ; effects 
of crossing, 60; a hybrid between 
the cowslip and primrose, 70 

Oxybaphus, 313 


181, 


Bs 


Peony, pollen-grains of, 338 

Parallelism between illegitimate and 
hybrid fertilisation, 239 

Pavonia, 313 

Phlox Hentzii, 120 

—- nivalis, 120 

subulata, 119, 287 

Planchon on Linum salsoloides, 100; 
L. Lewisii, 101; on Hugonia, 100 

Plantago lanceolata, 306 : 

media, 307 

Polemoniacezx, 118 


INDEX. 


POLLEN-GRAINS. 


Pollen-grains, relative diameter of, 
249 

Polyanthus, 18 

Polygonacex, 111 

Polygonum bistorta, 114 

fagopyrum, 111, 239; pollen- 
grains, 251 

Pontederia, 183; pollen-grains, 186; 
size of anthers, 252 

cordata, 187 

Posoqueria fragrans, 131 

Primrose, the common, 34, 57-71 

Primula, the, heterostyled species of, 
14; summary on, 45-49; homo- 
styled species, 49 

— auricula, 30, 43, 48, 74, 223 

—— equal-styled varieties, 273 

cortusoides, 44 

elata, 49 

elatior, Jacq., 32; relative fer- 

tility of the two forms, 33, 47; 

not a hybrid, 72, 73; equal-styled 

var. of, 224, 273 

farinosa, 45; equal-styled var., 
224, 273 

—— hirsuta, 74 

involucrata, 45 

longiflora, 50 

—— mollis, 49, 50 

Scotica, 49, 50 

—— Sibirica, 49 

— Sil:kimensis, 44, 47 

Sinensis, 22, 30, 38: relative 
fertility, 39-43, 47, 49; long- 
styled, 213; short-styled, 215; 
transmission of form, constitution 
and fertility, 216; equal-styled 
variety, 218-223, 273, 274 

—— stricta, 50 

— veris, 14: difference in struc- 
ture between the two forms, 15; 
degrees of fertility when legiti- 
mately or “legitimately united, 
25-52; fertility possessed by ille- 
gitimate plants, 228-234; equal- 
styled red variety, 234-238 ; long- 
styled, 241; length of pistil, 261, 
266 

vert cilluta, 49, 50 

villosa, 49 

vulgaris (var. acaulis Linn.), 

34; polien-grains, 35; relative fer- 


16 


SETHIA,. 


tility of the two forms, 37; length 
of pistil, 266 
Primula vulgaris,var. rubra, 224-228 
Prunella vulgaris, 299 
Psychotria, 135 
Pulmonaria angustifolia, 104, 239; 
anthers, 252, 287 
azurea, 110 
—— officinalis, 101, 238 ; number of 
flowers, 248; pistil, 250 


R. 


Ranunculus aquatilis, 311 

Ray-florets, their use, 5, 6 

lihamnus catharticus, 294, 307; size 

’ of corolla, 308 

frangula, 297 

— lanceolatus, 295 

Rhinanthus erista-galli, 4 

Rubiacex, 125, 131-136; size of 
anthers, 252; stigmas, 253; 
number of heterostyled genera, 
284, 285 

Rudgea eriantha, 135 

Rue, the common, 9 

Riuellia tuberosa, 329 


Salvia, 308 

cleistogama, 340 

Horminum, 8 

Satureia hortensis, 303, 304 

Scabiosa arvensis, 305 

atro-purpurea, 305, 307 

succisa, 305 

Seott, J.,on Primula auricula, 30, 
43, 223; P. vulgaris, 34; (var. 
rubra), 224; P. Sikkimensis, 44; 
P. farinosa, 45, 224; homostyled 
Primulx, 49,50; hybrids, 74, 75; 
length of pistil, 272; Hottonia 
palustris, 51; Androsace vital- 
liana, 53; Polyanthus, 58; Mit- 
chella repens, 127: _Acanthacex, 
313; Kranthemumambiguum bear- 
ing three kinds of flowers, 329 

Scrophularia aquatica, 147 

Serralula tinctoria, 280, 807 

Selina weuminata, 122 


INDEX. 


SETHIA. 


Sethia obtusifolia, 122 

Smith, Sir J. E., on the carrot, 8; 
hybrid Verbaseums, 76, 78; Ser- 
ratula tinctoria, 280; Cnicus, 
307; Subularia, 311 

Soldanella alpina, 54 

Specularia perfoliata, 330 

Spence, Mr., on Mollia, 168 

Spermacoce, 135 

Sprengel on Hottonia palustris, 51 

Stellaria graminea, 313 

Strawberry, the Hautbois, 293 

Subularia, 311 

Suteria, 131 


eS 


Thelymitra, 313 

Thomson, Dr., on Campanula, 530 

Thrum-eyed, origin of term, 14 

Thwaites, Mr., on ovules of Lim- 
nanthemum Indicum, 116 ; Sethia 
acuminata, 122; Discospermum, 
286 : 

Thymelia, 114 

Thymus citriodorus, 301 

serpyllum, 299, 301, 502, 304 

vulgaris, 302 

Timbal-Lagrayve, M., on hybrids in 
genus Cistus, 76 

Torrey, Dr., on Hottonia inflata, 
53, 313 

Transmission of the two forms of 
heterostyled plants, 268-270 

Treviranus on Androsace vital- 
liana, 53; Linum, 81 


V. 


Vandellia nummularifolia, 324 

sessiflora, 325 

Vaucher on the carrot, 8; Solda- 
nella alpina, 54; Lythrum sali- 
caria, 138, 144; L. thymifolia, 
165; Ilex aquifolium, 297; on 


WRAY. 


Labiate, 299; Viola hirta and 
collina, 317 

Verbaseum, wild hybrids of, 75-80 

lychnitis, 30, 76-78 

— pheniceum, 78 

thapsus, 76-79 

— virgatum, 78 

Viburnum, 6, 7 

Vicia, 327 

Villarsia, 116; anthers, 252 

Viola alba, 315, 320 

bicolor, 320 

— biflora, 320 

canina, 314, 321 

collina, 317 

— elatior, 320 

hirta, 318, 320 

zonodium, 320 

— lancifolia, 320 

mirabilis, 320 

nana, 319, 320; pollen-grains 
of, 338 oi 

— odorata, 317, 336 

palustris, 320 

Roxburghiana, 319 

—— fuppii, 320 

—— sylvatica, 320 

tricolor, 4, 320 

Voandzeia, 327 


w. 


Walnut, the, 10 

Watson, H. C., on cowslips, prim- 
roses, and oxlips, 57, 60, 63; 
Primula elatior, 72, 73 

Weddell, Dr., on hybrids between 
Aceras and Orchis, 76 

Wetterhan, Mr., on Corylus, 10 

Wichura, Max, on hybrid willows, 
76; sterile hybrids, 240 

Wirtgen on Lythrum *salicaria, 138, 
144, 148 

Wooler, W., on Polyanthus, 18 

Wray, Leonard, on Fragaria, 293 


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